US20150107496A1

US20150107496A1 - Biomass gasifier system for power generation

Info

Publication number: US20150107496A1
Application number: US14/513,496
Authority: US
Inventors: Krishna Kumar Bindingnavale Ranga
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-10-18
Filing date: 2014-10-14
Publication date: 2015-04-23

Abstract

The various embodiments herein provide an improved biomass based down draft gasifier for producing electrical energy. The gasifier comprises a reactor with double walled construction having an annular space between outer and inner shells. The annular space houses multiple helical guide vanes welded to the inner shell. The reactor is covered with a top cover assembly. An air inlet manifold is provided for directing the controlled air into the reactor through the air inlet nozzles. An automatic start system is provided for controlling the combustion of inlet fuel done with a spark plug. The gasifier comprises a throat which permits the ashes and charcoal of burnt fuel to drop into the bottom of the reactor. The gas separation holes are provided at the bottom of the reactor to separate the product gas from the charcoal. The product gas is taken out from an output pipe.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims the priority of the Indian Provisional Patent Application No. 1722/CHFJ2013 filed on Apr. 18, 2013, and postdated to Oct. 18, 2013 with the title “An Improved Biomass Gasifier System for Power Generation”, and the content of which is incorporated in entirety by reference herein.

BACKGROUND

1. Technical Field
The embodiments herein generally relate to the electrical power generation systems and particularly relates to a system and method for generating an electrical power through biomass. The embodiments herein more particularly relates to a method and a system for generating an electrical power using an efficient and improved down draft biomass gasifier with an Internal Combustion (IC) engine coupled to an electrical generator.
2. Description of the Related Art
Biomass gasifiers have been extant for many years and are manufactured in many countries by many manufacturers. Wood-based gasifiers were extensively used during the Second World War period (1939-1945) in Europe and elsewhere, to provide fuel gas for the petrol-engine based vehicles and electrical generators. There are principally two types of gasifiers, known as an up-draft gasifier and a down draft gasifier. The down draft gasifier is preferred for the IC engine applications, as the generated gas is relatively free of tar. The electrical generators equipped with gasifier have been manufactured in India for several years. They are mainly of the down draft type, and are coupled to the electrical generators equipped with IC engine.
The existing down draft type gasifier uses mild steel/carbon steel for the construction of reactor chamber walls. The usage of mild steel provides a short lifespan of around four to five years for the gasifiers. These gasifiers required a refractory lining to protect the mild steel from oxidation, which increases the maintenance and initial cost. Further the temperature of the output gases coming out of the output pipe is high and is in the range of 400-6000 C, which further needs to be cooled down by water. The volume of water commonly required for cooling the output gas is considerable. The gasifiers also have a welded bottom surface thereby providing difficulty in the cleaning and maintenance of the gasifiers. The gasifier needs to be inverted and then cleaned. Further, the existing literature does not discuss about a removal bottom and providing a stirrer.
Though, the existing down draft gasifiers have been used continuously, there are various drawbacks leading to an inefficient operation. The drawbacks include a continuous requirement of an operator throughout the day and night due to a lack of automated monitoring system and process. Further, a starting and stopping of the gasifier requires a laborious and dangerous process of manually lighting the gasifier using a burning torch, while managing several control valves. Also, in the existing gasifiers, a tar condensation inside the feed-hopper leads to a fuel clogging. Hence an extra vibrator is used to ensure a smooth feeding of the fuel. Other limitations of the existing gasifiers are clogging of scrub-water circuit with carry-over sediment and failure of stirring system at the bottom of the gasifier due to clogging.
Hence, there is a need for an improved and efficient gasifier system for generating electric power. Also there is a need for a method and system for automatically starting and stopping the gasifier based on running condition. Further, there is a need for a gasifier with simple construction to provide ease of usage and maintenance. Still further, there is need for a method for remotely monitoring the operations of a gasifier.

OBJECTIVES OF THE EMBODIMENTS

The primary object of the embodiments herein is to provide an improved and efficient down draft gasifier for generating the electrical energy.
Another object of the embodiments herein is to provide a method and system for remotely monitoring an operation of the down draft gasifiers.
Yet another object of the embodiments herein is to decrease temperature of output gas to an optimum level within the material limits of constructional parts of the down draft gasifier.
Yet another object of embodiments herein is to provide a system with a controlled air inlet to the reactor chamber of the down draft gasifier for a proper smoldering process.
Yet another object of the embodiments herein is to provide a system for remotely controlling the ignition and combustion process of the fuel with automatic, user friendly and nonhazardous operations.
Yet another object of the embodiments herein is to provide gasifier with a simple, adjustable and flexible construction facilitating ease of handling and maintenance.
Yet another object of the embodiments herein is to provide a gasifier with a helical guide for output gas flow to preheat the fuel thereby utilizing the heat of the output gas.
Yet another object of the embodiments herein is to provide a gasifier with an automatic start, run and shutdown operations using the state of art Programmable Logic controllers (PLC).
Yet another object of the embodiments herein is to provide a gasifier with safety trips to safely shut down the system automatically for a variety of out-of-limit operating parameters, including high reactor pressure, high reactor temperature, high water temperature, low water level, water pump failure, low frequency, high frequency, gas leakage, etc.
Yet another object of the embodiments herein is to provide a gasifier with an enhanced remote monitoring facility to minimize a manpower required, to allow a health parameter trending and failure prevention, to enhance uptime and to permit a system-wide management.
Yet another object of the embodiments herein is to provide a gasifier with a Polished Stainless Steel construction to provide a superior aesthetics design, corrosion and erosion resistant properties, negligible maintenance, extended life and smoother fuel feeding operation.
Yet another object of the embodiments herein is to provide a gasifier with a straight cylindrical design to improve fuel feeding operation, to prevent clogging and to eliminate a requirement for the vibrator.
Yet another object of the embodiments herein is to provide a gasifier with a double walled construction with gas flow in an annular region to provide an extended residence time for the output gas to encourage a drop-out of the particulates into an ash removal chute, to transfer the heat from the output gas to the fuel in the feed hopper to reduce a moisture content, to heat hopper inner wall to prevent condensation of tar and adhesion of wood chunks to the wall, to reduce the temperature of output gas, to minimizing water consumption, and to provide a higher efficiency due to a capture of heat in output gas back into the input fuel.
Yet another object of the embodiments herein is to provide a gasifier with a scrub-water cooling technology by radiator to eliminate spray-cooling, to reduce attendant water losses, and to minimize cooling water requirement.
Yet another object of the embodiments herein is to provide a gasifier with additional gas blowers and cyclonic separators to enhance a transient response with respect to load changes, to enhance purity of gas, to reduce a contamination load on water scrubber and to prevent clogging of venturi scrubber.
These and other objects and advantages of the embodiments herein will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

SUMMARY

The embodiments herein provide a down draft gasifier for generating energy. The gasifier comprises a reactor, a top cover assembly, an air inlet assembly, an automatic start unit, a stirrer assembly and a support system. The reactor is configured to smolder solid fuel to produce a product gas. The product gas is used to generate required energy. The top cover assembly arranged on top of the reactor is configured to provide protection to surrounding environment from any hazardous situations created in the reactor. The air inlet assembly is configured for directing a controlled air into a combustion zone of the reactor through a set of air inlet nozzles. The air is used for combustion of the solid fuel to produce the product gas. The automatic start unit is configured to control the combustion of the inlet solid fuel. The stirrer assembly configured to break the solid fuel into lumps for enabling the stable gas flow. The support system configured to sustain weight of the reactor assembly. The reactor is loaded with a solid fuel. The reactor is a double walled construction comprising an inner shell and an outer shell. The reactor further comprises a helical guide vane configured to assist a uniform flow of the product gas around the outer peripheral surface of the inner shell. The system comprises an output pipe mounted at extreme top end of the outer shell is configured to eject the product gas yielded from the reactor.
According to one embodiment herein, the top cover assembly is a spring loaded top cover which automatically opens during an overpressure or an explosion inside the reactor. The top cover assembly is fastened to a top flange of the reactor using a plurality of bolts. The top cover assembly is fastened in a circular manner so as to seal the top of reactor.
According to one embodiment herein, the air inlet assembly comprises an air inlet manifold provided at the outer surface of the outer shell. The air inlet manifold is configured to supply the air required for combustion of the fuel inside the reactor through a plurality of air inlet nozzles. The plurality of air inlet nozzles is configured to control the quantum of air into the reactor chamber and facilitate a quick replacement in case of corrosion.
According to one embodiment herein, the air inlet nozzle is adjustable to a required penetration inside the reactor before an initiation of the reactor. The air inlet nozzle is inserted into an outer pipe. The outer pipe is welded with the inner shell and housed inside a gland.
According to one embodiment herein, the gland allows a free thermal expansion of the air inlet nozzle and avoids formation of crack on the output pipe due to stress, heat and differential growth between the inner shell and the outer shell of the reactor.
According to one embodiment herein, the system further comprises an angular space between the outer shell and the inner shell of the reactor. The angular space houses the helical guide vanes which are welded to the inner shell of the reactor.
According to one embodiment herein, the helical guide vane is in the form of a multi strand thread to guide the product gas to flow in a helical pattern around the inner shell. The helical guide vanes increases residence time of the product gas inside the annular space and causes heat transfer from the product gas to the surroundings inner shell.
According to one embodiment herein, the system provides a gap of predetermined size between the inner surface of the outer shell and the helical guide vanes. The gap is configured to freely drop down ash and other solid condensable contaminants to bottom of the reactor.
According to one embodiment herein, the automatic start system comprises a Liquefied Petroleum Gas (LPG) fuel line connected to a burner assembly. The LPG is ignited by a built-in spark plug.
According to one embodiment herein, the system comprises a digital control system such as a Programmable Logic Circuits (PLC) for controlling the inlet of LPG and ignition of the spark plug. A control valve is provided to operate a start and stop of combustion process. The control valve is commanded by the digital control system.
According to one embodiment herein, the system comprises a suction blower configured to apply suction at the outer pipe. The suction draws the air from the burner and preheats the air to a predetermined temperature.
According to one embodiment herein, the system further comprises a lifting bracket configured to lift and place the gasifier from one location to another location. The lifting bracket is welded to the outer surface of the outer shell.
According to one embodiment herein, the system further comprises a hearth provided to support the fuel under combustion and permits a pile of glowing charcoal underneath. The charcoal filters the product gas by breaking down the tar into combustible compounds.
According to one embodiment herein, the system further comprises a plurality of radial gas separation holes provided in the wall of the inner shell of the reactor. The holes are configured to separate the product gas from the charcoal. The holes block the charcoal and permit only the product gas to exit from the inner shell to the annular space.
According to one embodiment herein, the stirrer assembly comprises a stirrer configured to stir the glowing charcoal bed so as to prevent blockages leading obstruction of gas flow. The stirrer is driven by a gear box connected to a motor, wherein the stirrer is rotated by the motor. The stirrer shaft passes through a plurality of glands and enters the bottom of the reactor.
According to one embodiment herein, the system further comprises an ash removal funnel placed in the annular space between the inner shell and the outer shell. The ash removal funnel is mounted on an ash removal flange. The ash removal funnel collects the ash dropped to the bottom of the reactor and the collected ash is taken out by the ash removal flange.
According to one embodiment herein, the support system comprises a plurality of support brackets which are sustained by a plurality of stands configured to support the reactor system.
According to one embodiment herein, the system further comprises a gas blower attached to the reactor which enhances start performance and transient response to the load changes. A cyclonic separator is configured to enhance the purity of gas by reducing contamination load on water scrubber and preventing the clogging of water scrubber.
According to one embodiment herein, the system further comprises an infrared laser beam configured to detect and indicate level of fuel consumption inside the reactor.
According to one embodiment herein, the system comprises a safety unit configured to automatically shutting down the reactor for a variety of out-of-limit operating parameters. The parameters include a high reactor pressure, a high reactor temperature, a high water temperature, a low water level, a water pump failure, a low frequency, a high frequency, a gas leakage and the like.
The embodiments herein provide an improved biomass based down draft gasifier for producing electrical energy. The improved down draft gasifier provides a simple construction with easily removable and adjustable components and a method for using the same. The down draft gasifier comprises a reactor with a double walled construction. The inner surface of the wall is referred to as an inner shell and the outer surface is referred to as an outer shell. The annular space between the outer shell and the inner shell houses a helical guide vanes welded to the inner shell. The top of the reactor is covered with a spring loaded top cover assembly. The down draft gasifier further comprises an air inlet manifold around the outer shell for directing a controlled air into a combustion zone of the reactor through a set of three or more air inlet nozzles. An automatic start system is also provided to control the combustion of inlet fuel and ignition of the fuel from a spark plug. The gasifier further comprises a throat which permits the ashes and charcoal of burnt fuel to drop to the bottom of the reactor. Plurality of Radial gas separation holes are provided on the wall of the inner shell which assists in separating a product gas from the charcoal. The product gas flows in the annular space between the inner and outer shells. The product gas is guided by the helical guide vanes to flow in a helical pattern around the inner shell.
According to one embodiment herein, a method for operating the improved down draft gasifier is provided. The method is categorized corresponding to four zones of operations comprising a drying zone, a distillation zone, a combustion zone and a char zone. In the drying zone, the solid fuels such as wood, rice husks, etc are used. The solid fuels of preferred sizes are selected based on the type of reactor and the corresponding configuration. The reactor of the gasifier is loaded with a solid fuel such as woody biomass, rise husks, etc and the top cover assembly is closed. The solid fuel undergoes heating to remove any moisture content by the product gas in the annular region.
According to one embodiment herein, the content of the fuel is extracted by the application of heat in the distillation zone. In the distillation zone, the solid fuel undergoes distillation by causing the volatile contents to become vaporized leaving behind the charcoal and ash. The heating is performed by a product gas in the annular space of the double layered wall. Also, the heat generated in the combustion zone also causes the above placed fuel to undergo a distillation process.
According to one embodiment herein, the combustion zone comprises smoldering of the fuel. In the combustion zone, the combustion of solid fuel is initiated by igniting a combustion gas from a spark plug. The combustion causes the smoldering of the fuel. When the top cover assembly is closed, the LPG is taken as input and is ignited by the spark plug. A suction is applied at the output pipe either by using a venturi scrubber or by a suction blower. The suction draws the air from the burner and preheats the air to a predetermined temperature such as around 5000-7000. The heated air enters into the air nozzle and is supplied to the fuel. The fuel undergoes combustion and with a controlled flow of air inside the reactor, smoldering of fuel is achieved. The fuel undergoes smoldering leaving behind the charcoal and ash. The charcoal and ash drops down from the hearth to the bottom of the reactor.
According to one embodiment herein, the gases produced in the combustion zone due to the smoldering enter into the char zone. In the char zone, the product gas is separated from the ashes and charcoal with the help of plurality of radial gas separation holes.
According to one embodiment herein, the product gases produced from the char zone flows into the annular region between the inner shell and outer shell. The product gas is guided by the helical guide vanes to flow in a helical pattern around the outer periphery of the inner shell towards the output pipe. The helical guide vanes also increase the residence time of the product gas within the annular region and enables the product gas to undergo a secondary reaction while moving upward through the annular region. In the secondary reaction, carbon dioxide reacts with oxygen to form carbon monoxide and water. The increased residence time of the product gas in the annular region transfers the heat to the fuel inside the inner shell for preheating and drying of the fuel and to the surrounding. This increases and enhances the efficiency of the gasifier. Once the fuel is consumed, the top cover assembly is opened and fuel is added.
According to one embodiment herein, regenerative heating is achieved by the double walled cylinders and the helical guide vanes. The product gas is cooled down significantly inside the annular region which also decreases the tar content. As the product gas moves upward in the annular space, the tar condenses on the inner surface of the outer shell and flows down to the bottom. The tar also experiences heat from the inner shell. The heat breaks down the long chain compounds of the tar into smaller compounds. The smaller compounds are also a form of a fuel. The temperature of the product gas is lowered significantly thereby leading to a minimal usage of water for cooling.
According to one embodiment herein, a set of helical guide vanes are provided within the annular space of the double layered wall. The helical guide vanes guide the product gas from the bottom of the reactor to the output pipe. The helical guide vanes increases the residence time of the product gas inside the annular space and thus causes the product gas to transfer the heat to the inner shell and to the surroundings. The increased residence time of the product gas also reduces its temperature thereby minimizing the usage of water to cool down the gas to a required temperature. The extended residence time at lower flow velocities encourages a drop-out of the particulates into an ash removal funnel. The heat transferred from the product gas to the fuel in the reactor helps to reduce a moisture content of the fuel. The heating of reactor inner shell prevents a condensation of tar and an adhesion of wood chunks to the inner shell. The double layered wall also minimizes water consumption and provides a higher efficiency due to a capture of the heat in product gas back into the input fuel.
According to one embodiment herein, the improved down draft gasifier comprises a safety feature for protection against an overpressure or explosion. The top cover assembly of the reactor comprises a spring loaded structure which automatically opens during an overpressure or an explosion inside the reactor.
According to one embodiment herein, a system and method for remotely controlling an input air into the reactor is provided. The system comprises an air inlet manifold fixed around the outer shell. The inlet manifold supplies the air to three or more inlet nozzles for the smoldering of the fuel inside the reactor. The usage of only one inlet manifold for supplying a required air inside the reactor provides a better control to an operator from a remote place. A digital control system is used for controlling the air inlet, spark plug and the control valve inside the reactor. Further, the air inlet nozzle is adjustable to a required penetration inside the reactor before the reactor is initiated.
According to one embodiment herein, the system and method facilitates turn-key operational ease, with plain language annunciation. The operation of the gasifier requires a minimum manpower and minimum training, ensures correct and safe procedures for start and stop, continuous automated safety and health monitoring, safety trips implemented and eliminates tar formation after shut-down. The gasifier adopts and implements safety trips for shutting down the reactor safely and automatically for a variety of out-of-limit operating parameters. The parameters include a high reactor pressure, a high reactor temperature, a high water temperature, a low water level, a water pump failure, a low frequency, a high frequency, a gas leakage, etc. An enhanced remote monitoring minimizes the manpower, allows health parameter trending and failure prevention, enhances uptime and permits system-wide management.
According to one embodiment herein, a polished stainless steel construction is provided to the down draft gasifier. The stainless steel provides superior aesthetics, corrosion resistant, negligible maintenance, extended life and smoother fuel feeding. The reactor is provided with a straight cylindrical design which improves fuel feeding and prevents clogging. Further, the straight design eliminates the need for a vibrator.
According to one embodiment herein, the product gas is cooled by scrubber water through radiator which eliminates spray-cooling and attendant water losses and minimizes a large requirement of water quantity.
According to one embodiment herein, a gas blower is added to the reactor which enhances a start performance, permits use of cyclonic separator, and enhances transient response to the load changes. The cyclonic separator enhances purity of gas, reduces contamination load on water scrubber, and prevents clogging of venturi scrubber. The welded stainless steel pipelines for product gases are compliant with international safety requirements.
According to one embodiment herein, an infrared laser beam is provided to detect and indicate a level of fuel consumption inside the reactor. The infra red lasers are used instead of visible-light laser and normal light because of their ability to penetrate through the smoke inside the reactor.
These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating the preferred embodiments and numerous specific details thereof, are given by way of an illustration and not of a limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:

FIG. 1 illustrates a cross sectional view of an improved down draft gasifier, according to one embodiment herein.

FIG. 2 illustrates a front view of a down draft gasifier with a system for filtering a product gas, according to one embodiment herein.

FIG. 3 illustrates a schematic view of an electrical power generation system with the down draft gasifier, according to one embodiment herein.

Although the specific features of the embodiments herein are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the embodiments herein.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
The various embodiments herein provide a down draft gasifier for generating energy. The gasifier comprises a reactor, a top cover assembly, an air inlet assembly, an automatic start unit, a stirrer assembly and a support system. The reactor is configured to smolder a solid fuel to produce product gas. The product gas is used to generate required energy. The top cover assembly arranged on top of the reactor is configured to provide protection to a surrounding environment from any hazardous situations created in the reactor. The air inlet assembly is configured for directing controlled air into a combustion zone of the reactor through a set of air inlet nozzles. The air is used for combustion of the solid fuel to produce the product gas. The automatic start unit is configured to control the combustion of the inlet solid fuel. The stirrer assembly configured to break the solid fuel into lumps for enabling the stable gas flow. The support system configured to sustain weight of the reactor assembly. The reactor is loaded with a solid fuel. The reactor is a double walled construction comprising an inner shell and an outer shell. The reactor further comprises a helical guide vane configured to assist a uniform flow of the product gas around the outer peripheral surface of the inner shell. The system comprises an output pipe mounted at extreme top end of the outer shell is configured to eject the product gas yielded from the reactor.
According to one embodiment herein, the top cover assembly is a spring loaded top cover which automatically opens during an overpressure or an explosion inside the reactor. The top cover assembly is fastened to a top flange of the reactor using a plurality of bolts. The top cover assembly is fastened in a circular manner so as to seal the top of reactor.
According to one embodiment herein, the air inlet assembly comprises an air inlet manifold provided at the outer surface of the outer shell. The air inlet manifold is configured to supply the air required for combustion of the fuel inside the reactor through a plurality of air inlet nozzles. The plurality of air inlet nozzles is configured to control the quantum of air into the reactor chamber and facilitate a quick replacement in case of corrosion.
According to one embodiment herein, the air inlet nozzle is adjustable to a required penetration inside the reactor before an initiation of the reactor. The air inlet nozzle is inserted into an outer pipe. The outer pipe is welded with the inner shell and housed inside a gland.
According to one embodiment herein, the gland allows a free thermal expansion of the air inlet nozzle and avoids a formation of crack on the output pipe due to stress, heat and a differential growth between the inner shell and the outer shell of the reactor.
According to one embodiment herein, the system further comprises an angular space between the outer shell and the inner shell of the reactor. The angular space houses the helical guide vanes which are welded to the inner shell of the reactor.
According to one embodiment herein, the helical guide vane is in the form of a multi strand thread to guide the product gas to flow in a helical pattern around the inner shell. The helical guide vanes increases a residence time of the product gas inside the annular space and causes a heat transfer from the product gas to the surroundings inner shell.
According to one embodiment herein, the system provides a gap of predetermined size between the inner surface of the outer shell and the helical guide vanes. The gap is configured to freely drop down ash and other solid condensable contaminants to bottom of the reactor.
According to one embodiment herein, the automatic start system comprises a Liquefied Petroleum Gas (LPG) fuel line connected to a burner assembly. The LPG is ignited by a built-in spark plug.
According to one embodiment herein, the system comprises a digital control system such as a Programmable Logic Circuits (PLC) for controlling the inlet of LPG and ignition of the spark plug. A control valve is provided to operate a start and stop of a combustion process. The control valve is commanded by the digital control system.
According to one embodiment herein, the system comprises a suction blower configured to apply suction at the outer pipe. The suction draws the air from the burner and preheats the air to a predetermined temperature.
According to one embodiment herein, the system further comprises a lifting bracket configured to lift and place the gasifier from one location to another location. The lifting bracket is welded to the outer surface of the outer shell.
According to one embodiment herein, the system further comprises a hearth provided to support the fuel under combustion and permits a pile of glowing charcoal underneath. The charcoal filters the product gas by breaking down the tar into combustible compounds.
According to one embodiment herein, the system further comprises a plurality of radial gas separation holes provided in the wall of the inner shell of the reactor. The holes are configured to separate the product gas from the charcoal. The holes block the charcoal and permit only the product gas to exit from the inner shell to the annular space.
According to one embodiment herein, the stirrer assembly comprises a stirrer configured to stir the glowing charcoal bed so as to prevent blockages leading obstruction of gas flow. The stirrer is driven by a gear box connected to a motor, wherein the stirrer is rotated by the motor. The stirrer shaft passes through a plurality of glands and enters the bottom of the reactor.
According to one embodiment herein, the system further comprises an ash removal funnel placed in the annular space between the inner shell and the outer shell. The ash removal funnel is mounted on an ash removal flange. The ash removal funnel collects the ash dropped to the bottom of the reactor and the collected ash is taken out by the ash removal flange.
According to one embodiment herein, the support system comprises a plurality of support brackets which are sustained by a plurality of stands configured to support the reactor system.
According to one embodiment herein, the system further comprises a gas blower attached to the reactor which enhances start performance and transient response to the load changes. A cyclonic separator is configured to enhance the purity of gas by reducing contamination load on water scrubber and preventing the clogging of water scrubber.
According to one embodiment herein, the system further comprises an infrared laser beam configured to detect and indicate level of fuel consumption inside the reactor.
According to one embodiment herein, the system comprises a safety unit configured to automatically shutting down the reactor for a variety of out-of-limit operating parameters. The parameters include a high reactor pressure, a high reactor temperature, a high water temperature, a low water level, a water pump failure, a low frequency, a high frequency, a gas leakage and the like.
The embodiments herein provide an improved biomass based down draft gasifier for producing electrical energy. The improved down draft gasifier provides a simple construction with easily removable and adjustable components and a method for using the same. The down draft gasifier comprises a reactor with a double walled construction. The inner surface of the wall is referred to as an inner shell and the outer surface is referred to as an outer shell. The annular space between the outer shell and the inner shell houses a helical guide vanes welded to the inner shell. The top of the reactor is covered with a spring loaded top cover assembly. The down draft gasifier further comprises an air inlet manifold around the outer shell for directing a controlled air into a combustion zone of the reactor through a set of three or more air inlet nozzles. An automatic start system is also provided to control the combustion of inlet fuel and ignition of the fuel from a spark plug. The gasifier further comprises a throat which permits the ashes and charcoal of burnt fuel onto the bottom of the reactor. Plurality of Radial gas separation holes are provided on the wall of the inner shell underneath the throat which assists in separating a product gas from the charcoal. The product gas is taken out from the double layered wall through a set of helical guide vanes to an output pipe.
According to one embodiment herein, a method for operating the improved down draft gasifier is provided. The method is categorized corresponding to four zones of operations comprising a drying zone, a distillation zone, a combustion zone and a char zone. In the drying zone, the solid fuels such as wood, rice husks, etc are used. The solid fuels of preferred sizes are selected based on the type of reactor and the corresponding configuration. The reactor of the gasifier is loaded with a solid fuel such as woody biomass, rise husks, etc and the top cover assembly is closed. The solid fuel undergoes heating to remove any moisture content by the product gas in the annular region.
According to one embodiment herein, the content of the fuel is extracted by the application of heat in the distillation zone. In the distillation zone, the solid fuel undergoes distillation by causing the volatile contents to become vaporized leaving behind the charcoal and ash. The heating is performed by product gas in the annular space of the double layered wall. Also, the heat generated in the combustion zone also causes the above placed fuel to undergo a distillation process.
According to one embodiment herein, the combustion zone comprises smoldering of the fuel. In the combustion zone, the combustion of solid fuel is initiated by igniting the combustion gas with the help of a spark plug. The combustion causes the smoldering of the fuel. When the top cover assembly is closed, the LPG is taken as input and is ignited by the spark plug. A suction is applied at the output pipe either by using a venturi scrubber or by a suction blower. The suction draws the air from the burner and preheats the air to a predetermined temperature such as around 5000-7000. The heated air enters into the air nozzle and is supplied to the fuel. The fuel undergoes combustion and with a controlled flow of air inside the reactor and a smoldering of fuel is achieved. The fuel undergoes smoldering leaving behind the charcoal and ash. The charcoal and ash drops down from the hearth to the bottom of the reactor inner shell.
According to one embodiment herein, the gases produced in the combustion zone due to the smoldering enter into the char zone. In the char zone, the product gas is separated from the ashes and charcoal with the help of radial gas separation holes provided in the wall of the inner shell.
According to one embodiment herein, the product gases produced from the char zone flows into the annular region between the inner shell and outer shell. The product gas is guided by the helical guide vanes to flow in a helical pattern around an outer periphery of the inner shell to the output pipe. The helical guide vanes also increase the residence time of the product gas within the annular region and enables the product gas to undergo a secondary reaction while moving upward through the annular region. In the secondary reaction, carbon dioxide reacts with oxygen to form carbon monoxide and water. The increased residence time of the product gas in the annular region transfers the heat to the fuel inside the inner shell for preheating and drying of the fuel and to the surrounding. This increases and enhances the efficiency of the gasifier. Once the fuel is consumed, the top cover assembly is opened and a new fuel is added.
According to one embodiment herein, a regenerative heating is achieved by the double walled cylinders and the helical guide vanes. The product gas is cooled down drastically inside the annular region which also decreases the tar content. As the product gas moves upward in the annular space, the tar condenses on the inner surface of the outer shell and flows down to the bottom. The tar also experiences heat from the inner shell. The heat breaks down the long chain compounds of the tar into smaller compounds. The smaller compounds are also a form of a fuel. The temperature of the product gas is lowered significantly thereby leading to a minimal usage of water for cooling.
According to one embodiment herein, a set of helical guide vanes are provided within the annular space of the double layered wall. The helical guide vanes guide the product gas from the bottom of the reactor to the output pipe. The helical guide vanes increases the residence time of the product gas inside the annular space and thus causes the product gas to transfer the heat to the inner shell and to the surroundings. The increased residence time of the product gas also reduces its temperature thereby minimizing the usage of water to cool down the gas to a required temperature. The extended residence time at lower flow velocities encourages a drop-out of the particulates into an ash removal funnel. The heat transferred from the product gas to the fuel in the reactor helps to reduce a moisture content of the fuel. The heating of reactor inner shell prevents a condensation of tar and an adhesion of wood chunks to the inner shell. The double layered wall also minimizes water consumption and provides a higher efficiency due to heat capture from product gas back into the input fuel.
According to one embodiment herein, the improved down draft gasifier comprises a safety feature for protection against an overpressure or explosion. The top cover assembly of the reactor comprises a spring loaded structure which automatically opens during an overpressure or an explosion inside the reactor.
According to one embodiment herein, a system and method for remotely controlling an input air into the reactor is provided. The system comprises an air inlet manifold fixed around the outer shell. The inlet manifold supplies the air to three or more inlet nozzles for the smoldering of the fuel inside the reactor. The usage of only one inlet manifold for supplying required air inside the reactor provides a better control to an operator from a remote place. A digital control system is used for controlling the air inlet, spark plug and the control valve inside the reactor. Further, the air inlet nozzle is adjustable to a required penetration inside the reactor before the reactor is initiated.
According to one embodiment herein, the system and method facilitates turnkey operational ease, with plain language annunciations. The operation of the gasifier requires a minimum manpower and minimum training, ensures correct and safe procedures for start and stop, continuous automated safety and health monitoring, safety trips implemented and eliminates tar formation after shut-down. The gasifier adopts and implements safety trips for shutting down the reactor safely and automatically for a variety of out-of-limit operating parameters. The parameters include a high reactor pressure, a high reactor temperature, a high water temperature, a low water level, a water pump failure, a low frequency, a high frequency, a gas leakage, etc. An enhanced remote monitoring minimizes the manpower, allows health parameter trending and failure prevention, enhances uptime and permits system-wide management.
According to one embodiment herein, a polished stainless steel construction is provided to the down draft gasifier. The stainless steel provides superior aesthetics, corrosion resistant, negligible maintenance, extended life and smoother fuel feeding. The reactor is provided with a straight cylindrical design which improves fuel feeding and prevents clogging. Further, the straight design eliminates the need for a vibrator.
According to one embodiment herein, the product gas is cooled by scrubber water through radiator which eliminates spray-cooling and attendant water losses and minimizes a large requirement of water quantity.
According to one embodiment herein, a gas blower is added to the reactor which enhances a start performance, permits use of cyclonic separator, and enhances transient response to the load changes. The cyclonic separator enhances purity of gas, reduces contamination load on water scrubber, and prevents clogging of venturi scrubber. The welded stainless steel pipelines for product gases are compliant with international safety requirements.
According to one embodiment herein, an infrared laser beam is provided to detect and indicate a level of fuel consumption inside the reactor. The infrared lasers are used instead of visible-light laser and normal light because of their ability to penetrate through the smoke inside the reactor.
FIG. 1 illustrates a cross sectional view of an improved down draft gasifier, according to one embodiment herein. The down draft gasifier 100 comprises a reactor chamber formed by an outer shell 103 and an inner shell 104. The outer shell 103 and the inner shell 104 create an annular space 121 in between thereby providing a double walled construction to the reactor. The outer shell 103 and the inner shell 104 are manufactured from Austentic stainless steel for providing a protection against corrosion and erosion. The outer shell 103 also assists in radiating an excessive heat from a product gas to the surroundings. The thickness of the inner shell 104 is greater than that of the outer shell 103 for providing a longer life to the reactor. The inner shell 104 is subjected to very high reactor temperatures of around 10000 Celsius. The inner shell 104 is able to withstand the inner reducing atmosphere of hydrogen and carbon monoxide without requiring any refractory lining.
A lifting bracket 102 is welded to the outer surface of the outer shell 103. The lifting bracket 102 allows the gasifier 100 to be lifted and placed from one location to another location. The product gas yielded from the down draft reactor is taken out through an output pipe 123. The output pipe 123 is mounted at extreme top end of the outer shell 103. The position of the output pipe 123 provides a high residence time to the product gas inside the annular space 121 between the outer shell 103 and the inner shell 104. The high residence time also enables the product gas to complete all water gas reactions and transfer maximum heat to the inner shell 104. The temperature of the product gas taken out from the output pipe 123 is reduced significantly to lower than hundred degrees Celsius. The top of the reactor is covered with a top cover assembly 101. The top cover assembly 101 is fastened to the top flange by means of bolts 124 in a circular manner and thereby seals the top of the reactor. The top cover assembly 101 is a spring loaded top cover providing a protection against over pressure due to any explosion or configuration of the reactor.
The outer surface of the inner shell 104 is welded with plurality of helical guide vanes 122. The helical guide vanes 122 are in the form of multi strand thread which assists a uniform flow of product gas around the outer peripheral surface of the inner shell 104. The helical guide vanes 122 enhance the heat dissipation of the product gas by transferring heat to the fuel inside the inner shell 104 and to the surroundings. The helical guide vanes 122 increases the residence time of the product gas for completing all the water gas reactions and further lowers the output temperature of the product gas before exiting the reactor. The helical guide vanes 122 are arranged in a manner that no contact is made with the inner surface of the outer shell 103. A gap of predetermined size is provided between the inner surface of the outer shell 103 and the helical guide vanes 122 to permit the ash and other solid contaminants to drop down to the bottom of the reactor. The gap also permits any condensed or condensable material such as tar to freely flow down from the inner surface of the outer shell 103 to the bottom of the reactor.
The down draft gasifier 100 further comprises an air inlet manifold 120 provided at the outer surface of the outer shell 103. The air inlet manifold 120 provides the required air for the combustion of the fuel inside the reactor through a set of three or more air inlet nozzle 108. The common air inlet manifold 120 provides an ease of starting and shutdown of the reactor by controlling a single control valve 105. The design of air inlet nozzle 108 facilitates a quick replacement in case of corrosion and also provides a control to adjust the quantum of air into the reactor chamber. The air inlet nozzle 108 is inserted into an outer pipe 106. The outer pipe 106 is welded with the inner shell 104 and housed inside a gland 107. The gland 107 is fixed to the outer shell 103. The gland 107 allows a free thermal expansion and avoids a formation of crack of the output pipe due to stresses, heat and a differential growth between the inner shell 104 and the outer shell 103 of the reactor. The gland 107 allows a free expansion of the air inlet nozzle 108. The air inlet nozzle 108 fits inside the air inlet pipe and penetrates inside the fuel. The air inlet nozzle 108 penetrates to a predetermined extent inside the reactor based on the type of fuel. The air inlet nozzle 108 allows for adjusting the temperature of the fuel, adjusting the size of the air nozzle tip for controlling the power output from the reactor with a quick replacement feature.
The down draft gasifier 100 further comprises an automatic start system 119. The automatic start system 119 comprises a Liquefied Petroleum Gas (LPG) fuel line connected to a burner assembly. The LPG is ignited by a built-in spark plug. The inlet of LPG and the ignition of the spark plug are commanded from a digital control system such as a Programmable Logic Circuits (PLC). A control valve 105 is opened during start of the combustion process and closed for stopping the same process. The control valve 105 is also commanded by the digital control system. A hearth or throat 118 is provided to support the fuel under combustion and permits the pile of glowing charcoal underneath. The charcoal filters the gases and breaks down tar into combustible compounds. The hearth 118 is not welded to the reactor and is easily removable. The hearth 118 is removable for treating the corrosion at high temperatures and for periodic cleaning of the reactor. The reactor system is supported on two or more support brackets 117. The support brackets 117 are sustained on same number of stands 113. A plurality of Radial gas separation holes 116 are provided in the wall of the inner shell of the reactor. The holes 116 separate the product gas from the charcoal by blocking the charcoal and permitting only the product gas to exit from the inner shell 104 to the annular space 121. Further, at the bottom of the reactor, glands for a stirrer 115 are provided. The stirrer 115 is driven by a gear box 112 connected to a motor 114. The stirrer 115 shaft passes through the glands and enters the bottom of the reactor. The stirrer shaft is rotated by means of motor 114 coupled to the gear box 112. The bottom of the doubled layered wall functions an ash removal funnel 110. The ash removal funnel 110 is formed in the annular space 121 between the inner shell 104 and the outer shell 103. The constructional design of the ash removal funnel 110 allows easy mounting of bottom flange and also easy and free removal of the bottom flange. The ash removal funnel 110 assembly also allows easy mounting and dismounting of stirrer 115 assembly along with the bottom flanges. The removable stirrer 115 assembly and the bottom flanges also allow an easy cleaning of the reactor. The bottom of the ash removal funnel 110 is mounted with an ash removal flange 111. The ash dropped in the ash removal funnel 110 is collected at the removal flange 111 and then is taken out by an ash removal system. A set of bolts closes/seals the inner shell 104 with the bottom flange.
FIG. 2 illustrates a system for filtering a product gas obtained from the down draft gasifier, according to one embodiment herein. The output pipe of the gasifier 100 is connected with a venturi scrubber 201. The venturi scrubber 201 removes any fine particle of ashes or other solid particles carried forward by the product gas. The producer gas is then passed through a sawdust filter 202 for further removing any remaining insoluble part of the tar or any carry-over sediments. The soluble tar or particles are captured in the water storage tank 205. The water is recycled and is again used in the same water tank. The insoluble tar is removed from by using a filter bed. The product gas is then finally passed through a fabric filter 203. The fabric filter 203 removes any left out particles from the product gas. The product gas from the fabric filter 203 is directed to an IC engine for generating electric power.
FIG. 3 illustrates a system for generating electric power from the producer gas obtained from the down draft gasifier, according to one embodiment herein. The down draft gasifier 100 is operated and product gas is obtained from the output pipe. The producer gas goes through plurality of filtration process and is passed into an internal combustion (IC) engine 302. The product gas undergoes combustion in the IC engine 302 which drives a generator for generating electric power. A control panel 301 is used which controls the output of the generator.
The embodiments herein provide an improved and efficient gasifier system for generating electric power. The system provides a system for remotely monitoring an operation of the down draft gasifiers and accordingly decrease a temperature of an output gas to an optimum level. The system provides the gasifier with a helical guide for output gas flow to preheat the fuel thereby utilizing the heat of the output gas. The remote monitoring facility of the gasifier minimizes the requirement of manpower and automates the failure prevention, to enhance uptime and to permit a system-wide management. The gasifier is provided with a Polished Stainless Steel construction to provide a superior aesthetics design, corrosion and erosion resistant properties, negligible maintenance, extended life and smoother fuel feeding operation. The gasifier facilities a drop-out of the particulates into an ash removal chute and to transfer the heat from the output gas to the fuel in the feed hopper to reduce moisture content. The system transfers the heat to a hopper inner wall to prevent condensation of tar and adhesion of wood chunks to the wall. The system reduces the temperature of output gas and minimizes water consumption used for cooling down the output gas. The system provides a higher efficiency due to the capture of heat in product gas back into the input fuel.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.
It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications.
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

Claims

What is claimed is:

1. A down draft gasifier for generating energy comprising:

a reactor assembly comprising an inner shell, an outer shell, a helical guide vane, and an output pipe, and wherein the reactor is a double walled construction, and wherein the reactor is loaded with a solid fuel, and wherein the reactor is configured to smolder a solid fuel to produce a product gas, wherein the product gas is used to generate a required energy and wherein the helical guide vane is configured to assist a uniform flow of the product gas around an outer peripheral surface of the inner shell, and wherein the output pipe is mounted at extreme top end of the outer shell to eject the product gas yielded from the reactor;

a top cover assembly arranged on the top of the reactor, configured to provide protection to surrounding environment from any hazardous situations created in the reactor;

an air inlet assembly configured for directing a controlled air into a combustion zone of the reactor through a set of air inlet nozzles, wherein the air is used for combustion of the solid fuel to produce the product gas;

an automatic start unit configured to control the combustion of the inlet solid fuel;

a stirrer assembly configured to break the solid fuel into lumps for enabling the stable gas flow, and

a support system configured to sustain a weight of the reactor assembly.

2. The system according to claim 1, wherein the top cover assembly is a spring loaded top cover which automatically opens during an overpressure or an explosion inside the reactor, wherein the top cover assembly is fastened to a top flange of the reactor using a plurality of bolts, wherein the top cover assembly is fastened in a circular manner so as to seal the top of reactor.

3. The system according to claim 1, wherein the air inlet assembly comprises an air inlet manifold provided at the outer surface of the outer shell, wherein the air inlet manifold is configured to supply the air required for combustion of the fuel inside the reactor through a plurality of air inlet nozzles, wherein the plurality of air inlet nozzles are configured to control a quantum of air into the reactor chamber and facilitate a quick replacement in case of corrosion.

4. The system according to claim 1, wherein the air inlet nozzle is adjustable to penetrate inside the reactor by a required distance before an initiation of the reactor, and wherein the air inlet nozzle is inserted into an outer pipe, and wherein the outer pipe is welded with the inner shell and housed inside a gland.

5. The system according to claim 1, wherein the gland allows a free thermal expansion of the air inlet nozzle and avoids a formation of crack on the output pipe due to stress, heat and a differential growth between the inner shell and the outer shell of the reactor.

6. The system according to claim 1, further comprises an angular space between the outer shell and the inner shell of the reactor, wherein the angular space houses the helical guide vane, wherein the helical guide vane is welded to the inner shell of the reactor.

7. The system according to claim 1, wherein the helical guide vane is in arranged in a form of a multi strand thread to guide the product gas to flow in a helical pattern around the inner shell, wherein the helical guide vane increases a residence time of the product gas inside the annular space and causes a heat transfer from the product gas to the surroundings inner shell.

8. The system according to claim 1, further provides a gap of predetermined size between the inner surface of the outer shell and the helical guide vanes, wherein the gap is configured to freely drop down to ash and other solid condensable contaminants to the bottom of the reactor.

9. The system according to claim 1, wherein the automatic start system comprises a Liquefied Petroleum Gas (LPG) fuel line connected to a burner assembly, wherein the LPG is ignited by a built-in spark plug.

10. The system according to claim 1, further comprises a digital control system such as a Programmable Logic Circuits (PLC) for controlling the inlet of LPG and ignition of the spark plug, wherein a control valve is provided to operate a start and stop of combustion process, wherein the control valve is commanded by the digital control system.

11. The system according to claim 1, further comprises a suction blower configured to apply suction at the outer pipe, wherein the suction draws the air from the burner and preheats the air to a predetermined temperature.

12. The system according to claim 1, further comprises a lifting bracket configured to lift and place the gasifier from one location to another location, wherein the lifting bracket is welded to the outer surface of the outer shell.

13. The system according to claim 1, further comprises a hearth provided to support the fuel under combustion and permits a pile of glowing charcoal underneath, wherein the charcoal filters the product gas by breaking down the tar into combustible compounds.

14. The system according to claim 1, further comprises a plurality of radial gas separation holes provided in the wall of the inner shell of the reactor, wherein the holes are configured to separate the product gas from the charcoal, wherein the holes block the charcoal and permit only the product gas to exit from the inner shell to the annular space.

15. The system according to claim 1, wherein the stirrer assembly comprises a stirrer configured to stir the glowing charcoal bed so as to prevent blockages leading obstruction of gas flow, wherein the stirrer is driven by a gear box connected to a motor, wherein the stirrer is rotated by the motor, wherein the stirrer shaft passes through a plurality of glands and enters the bottom of the reactor.

16. The system according to claim 1, further comprises an ash removal funnel placed in the annular space between the inner shell and the outer shell, wherein the ash removal funnel is mounted on an ash removal flange, wherein the ash removal funnel collects the ash dropped to the bottom of the reactor and the collected ash is taken out by the ash removal flange.

17. The system according to claim 1, wherein the support system comprises a plurality of support brackets, wherein the support brackets are sustained by a plurality of stands configured to support the reactor system.

18. The system according to claim 1, further comprises a gas blower attached to the reactor which enhances a start performance and transient response to the load changes, wherein a cyclonic separator is configured to enhance the purity of gas by reducing contamination load on water scrubber and preventing the clogging of water scrubber.

19. The system according to claim 1, further comprises an infrared laser beam configured to detect and indicate the level of fuel consumption inside the reactor.

20. The system according to claim 1, comprises a safety unit configured to automatically shutting down the reactor for a variety of out-of-limit operating parameters, wherein the parameters include a high reactor pressure, a high reactor temperature, a high water temperature, a low water level, a water pump failure, a low frequency, a high frequency, a gas leakage.