GR20190100160A - Automatic system for the neutralization of ship chimney's gaseous pollutants - simultaneous energy recovery - Google Patents

Abstract

An automatic system neutralizing gaseous pollutants derived from gas chimneys and simultaneous energy recovery are disclosed. The invention is characterized in that the unit consists of submersible pumps of suitable supply and pressure, which pumps supply the tank (1) for the operation of the desalinator (2) via the reverse osmosis process. The desalinated water is drained into a tank (3) where an appropriate amount of alkaline solution will be poured, preferably NaOH with suitable pH through a dosing pump (4) supplied by the NaOH tank (5); in the sequel, the alkaline solution -through a pump (6) with suitable pressure- will be sprayed in three places for the cationization of the exhaust gases: the first place is downstream of the exhaust gases inlet in the venturi (8) pipe in the pre-treatment phase; the second place is the first stage of the treatment-cationization of the scrubber (10); the third place is the second cationization stage of the scrubber. The exhaust gases will be released into the atmosphere free of S while the washing water will be collected in a tank (12) where the oily matter and particles will be separated in the selected tank (13) as stock to be delivered at the selected port and the wash water is led to the sea/wash water heat exchanger (14); the sea water returns to the sea and the treated wash water is taken at a lower temperature to the tank (3) for the circuit to be closed. Complete renewal of all used water is carried out every hour. The reduction of the exhaust gases of the chimney is achieved through a thermal exhaust / water exchanger (15) in which the exhaust gases are driven through a bypass equipped with pneumatic valves through which the exit of the exhaust gases returns to its previous state. The produced steam is partly driven into a steam turbine (16) connected to the generator (17) for power generation and partial fuel oil liquefaction.

Description

AUTOMATIC SYSTEM FOR NEUTRALIZATION OF GASEOUS POLLUTANTS FROM SHIP CHIMNEYS WITH SIMULTANEOUS ENERGY RECOVERY

DESCRIPTION

The exhaust gases coming out of ship chimneys contain SOx, NOx and other volatile hydrocarbons as a consequence of combustion.

The concentration of SOx in the waste gas is high, because the content of S contained in the fuel (fuel oil-heavy fuel) reaches up to 4%.

In general, the purification of waste gases from SOx with an efficiency of 99% is achieved by a cationization process.

In order to achieve a high efficiency in cleaning, the temperature of the exhaust gases containing SOx must be low because otherwise the degree of saturation of the droplets will be small and consequently the efficiency of the precipitation of SOx will be small.

And their speed must exceed 3 m/sec, in order to achieve the complete mixing-washing of the gases with the droplets of the alkaline NaOH solution and to precipitate the SOx in the form of sodium sulfate and sodium sulfite.

And this is because the size of the molecules of the waste gases are orders of magnitude smaller than the size of the molecules of the solution.

And according to statistical thermodynamics the potential collision-mixing of these two fluids becomes more likely if the size of their molecules fluctuates at approximately the same level. That is, in the same order of size of the molecules.

And in order to achieve the reduction of the order of size of the droplets of the alkaline solution, so that the difference does not exceed two orders of size between them, we pour with high pressure which means a high speed of the droplets, so as to reduce the size of the droplets to a minimum and the contact surface will increase. And so this contact will be achieved which will bring about the precipitation of the sulfur contained in S03 and which will be converted first into H2SO4 and then into NaS04 according to the following chemical reactions.

SO3+H2O → H2SO4

H2SO4+ NaOH → Na2SO4

In addition, it should be pointed out that the temperature of the exhaust gases ranges from 450 °C - 430 °C and to reduce this temperature as much as possible, e.g. to 160 °C, so as to increase the degree of saturation, i.e. the capture of S under form of sulfate with the cationization process in which it is required to spend a large amount of water which will evaporate to further reduce the temperature of the waste gases.

And if used

1) Desalinated water to avoid operational complications and to avoid acquiring large amounts of salt as a result of evaporation, due to the need to use many cubic meters of water will increase operating costs, such as electricity for the reverse osmosis process.

2) Sea water will cause complications in the operation of the unit due to the accumulation of Ca2SO4, Ca2CO3 salts in the washer-scrubber as well as in the venturi tube that is upstream of it.

The produced heat that must be extracted from a diesel engine of e.g. 10MW is equal to Q=m cpΔΤ=75,000kg x x0.24kcal/kg.°C(430°C -250°C)=3,240,000kcal/h We can with an energy recuperator and specifically a water/flue gas heat exchanger to reduce - kidnap - recover part of the huge energy that is lost by saving fuel for the ship's propulsion and at the same time to reduce the temperature of the waste gases which is the primary goal. This is achieved as follows.

In the chimney of the ship, specifically at the appropriate level of the ship, we make a by pass, so as to divert and force the flow of exhaust gases to pass through a heat exchanger in flow, through the courtyards, and the water outside them, as illustrated in figure 2 and in its section figure 3.

We cannot further reduce the exit temperature of the exhaust gases because there is the risk of liquefaction of the tar substances contained in the exhaust gases and of them adhering to the pipes-courtyards of the heat exchanger figure 2 and figure 3, where they will pass which will then drastically reduce the heat transfer coefficient to water.

That is why we are limited to e.g. 250°C, in order to ensure the long-term operation of the unit avoiding possible problematic maintenance and at the same time energy will be saved equal to Q=m cpΔΤ=75.000kg x0.24kcal/kg.°Cx(430° C -250°C)=3,240,000kcal/h with Q=3,240,000kcal/h which given that the lower calorific value of fuel oil is equal to 8000kcal/h

, corresponds to a saving of 405kg/h fuel oil.

The steam produced by the heat exchanger ranges at 5,800 kg/h.

Of which 1000kg/h will feed the heating system to liquefy the fuel oil and 2,240,000kcal/h will remain to be introduced to the steam turbine for energy production.

This means firstly that the steam produced from the recovery will eliminate the use of the fuel oil consuming steam generator to preheat and liquefy the fuel oil required to enter the diesel engines and secondly by injecting this excess steam into a steam turbine it will produce auxiliary power to the diesel engines for the ship's propulsion or completely for the operation of the ship's high power generators.

Due to the high revolutions of the steam turbine shaft which range at 5200rpm it will mate with Vi speed reducer gear to mate with the electric generator whose number of revolutions range at 2400rpm.

The power of the steam turbine with the above assumptions and for the specific case and for the given propulsion power will vary at 0.5 MW.

The circuit is closed and the water is deionized.

It should also be pointed out that by using a type 0.5 diesel fuel with a much lower concentration of S, which means that we are free from the risk of acquiring tar substances, we can reduce the exit temperature of the exhaust gases, for example, from 250 °C to 130 °C and thus will cut AT=430°C -130°C =300°C and which translates into energy savings Q=m cpΔΤ=75,000kg x.24kcal/kg.°C(430°C -130°C)=5,400,000kcal /h. And because the resulting steam varies at 10,000kg/h and the power P=ΜxΔητ/860=ΜxΔη/1000 with ητ=0.86 results in 0.8MW.

The energy saved from the operation of the ships increases with the power of the diesel propulsion engines.

This means that the energy saving and production system for the ship may well operate independently if there is no need to neutralize SOx

The operation of the arrangement is as follows.

We place on the deck or in a suitable place an appropriately dimensioned water/exhaust heat exchanger.

From where the main water enters at 15°C and exits vaporized at 250°C, and the exhaust gases enter at 430°C and exit at e.g. 250°C. They enter the upper end of the venturi tube and are then led to the lower end of the washer-scrubber.

This cationization in the scrubber will be done in two stages, so that any amount of gas that has escaped the treatment in the first stage will undergo the treatment in the second stage and thus achieve the complete precipitation of SOx.

When the exhaust gases pass through the first stage, a VENTURI tube will be placed above it which, after the exhaust gases enter it, will also have a cationization system with the same alkaline solution, so that primarily the temperature will be reduced by the 430 °C at (180-170 )°C.

The ionization water will come from seawater supplied by submersible pumps and after passing through a desalination system with reverse osmosis, an appropriate amount of NaOH will be added, so that the resulting solution is alkaline with a suitable pH.

This alkaline solution will be poured under appropriate pressure perpendicular to the turbulent flow of the exhaust gases, so as to avoid the passage of untreated exhaust gases to the atmosphere.

The particles as well as the oily and tar substances that precipitate together with the aqueous solution which now contains sodium sulfate and sulphite salts are led to a collection tank in which the oily and tar substances float and which through a separator we lead the oily and tar substances substances in a tank of suitable size and which will be supplied for further processing in a port.

And the treated water, because it is at a higher temperature through a heat exchanger (14) with sea water, in reverse flow will reduce its temperature.

Then by adding a small amount of the same alkaline solution, it will give the same chemical characteristics to the solution and thus the operation of the washing machine will continue in a closed circuit as shown in figure 1.

After they enter the entrance of the venturi tube and undergo a pre-treatment, i.e. a first cationization with an alkaline NaOH solution.

Then, through the pipe connection, the outgoing exhaust gases will enter the first stage of cationization with the same alkaline solution and after complete mixing of the molecular groups of the exhaust gases with the cloud of droplets of the alkaline solution, the exits of the first stage undergo a similar washing in the second stage continuously of the first one with the same alkaline solution. After that, they exit to the atmosphere free of 99% of S.

It should be noted that the aforementioned calculations for a specific ship propulsion power equal to 10MW were made to make the method and concept clear and understandable. But the methodology and process of SOx neutralization with simultaneous energy recovery remains unchanged for any ship's propulsion power. It should also be noted that the bypass with which the chimney is equipped so that the flue gases pass through the heat exchanger using on-off pneumatic valves (21), (20), if for any malfunction e.g. blockage by particles or bituminous substances, the exhaust gas drainage through the heat exchanger is automatically interrupted and returns to the previous state by closing (20) and opening (21).

Cleaning the exhaust passageways is achieved by removing the exchanger covers and using an iron brush

The description of the operation of the unit is as follows.

We put the unit into operation and the submersible pumps that every ship is equipped with automatically work and transfer sea water from the sea level to the tank (1) on the deck.

From this tank, water is pumped to pass through the desalination system (2) with membranes in a double stage and the sludge is discharged into the sea, and the desalinated water is placed in a tank (3) where NaOH is poured with a dosing pump (4). so that the pH of the resulting aqueous solution is of the desired degree of alkalinity using the alkalinity control system (25). The dosing pump supplies the caustic soda from the special tank (5), where NaOH is contained.

From the tank (3) through a pump (6) at a suitable pressure three positions are supplied for the cationization of the exhaust gases and which are the first downstream (7) of the exhaust gas inlet in the venturi tube (8) in the pretreatment phase.

In the second which is the first stage (9) treatment-cationization of the scrubber (10). And in the third position (11) which is the second cationization stage of the washer-scrubber. It should also be noted that the alkali solution ejectors shall be properly constructed and operated so that the ejector is perpendicular to the exhaust gas flow and creates a turbulent flow to increase turbulence with the ultimate goal of maximizing surface area. mixing of molecular droplets and molecular gas aggregates, for the effective precipitation of S .

The exhaust gases after passing through the venturi tube and then passing through the first and second stage of cationization will exit to the atmosphere at about (70-80)°C, and free of S.

The residual wash water together with the particles and the oily and tarry substances will be collected in a tank (12), from where the floating oily and tarry substances are immediately separated and will be stored in another tank (13) for delivery to the selected port. and the wash water, which has a temperature varying between (80-90) °C, is led to a heat exchanger (water/water) (14) in which the heat of the wash water is extracted, through seawater at a temperature of about 15°C, so that the recycled water enters the tank (3) at the same temperature.

In this way, the demand for desalinated water and consequently the energy consumption becomes minimal as well as for this caustic soda, because the PH of the recycled water is alkaline. Every hour the total water used is completely renewed. The amount of water used is minimal compared to what is available and this has as a consequence the economic operation of the device.

Keeping neutralization effectiveness unchanged over time.

At the same time, the exhaust gases from the diesel engine entering the heat exchanger (15) (air/water) assign their heat load to the water which is vaporized and the vapor of which in sufficient quantity is first drained into the fuel oil liquefaction system, with which it is equipped all ships that use heavy fuel.

With the remaining mass of steam we feed a steam turbine (16) with a suitable reducer connected to it with which the generator (17) is paired.

When the gases leave the bypass-by pass and enter the original chimney, we create a deceptive outlet on the chimney to the atmosphere (22), to avoid creating back pressure in the diesel engine.

And the exhaust gases due to the negative pressure created by the venturi tube will be absorbed towards the exit from the scrubber, entraining with them a quantity of atmospheric air which will act beneficially by reducing the temperature of the exhaust gases and becoming suitable temperatures for the treatment of cationization.

Upstream of the deceptive exit there will be another bypass from the chimney (by pass), equipped with pneumatic valves (23), (24) through which the exhaust gases are led to the venturi-scrubber cationization system (10) and exit of the freed from S of exhaust gases.

There will be two pneumatic on-off valves (23), (24) with which it will be possible to automatically return to the previous operating state.

With this system, the neutralization of SOx is solved independently at the same time with simultaneous energy recovery.

With our proposed system of desulfurization of the exhaust gases from the ships' chimneys with simultaneous energy recovery, the problem of sulfur precipitation efficiency (in the form of binding to sulfates and sulphites) is fundamentally solved with an efficiency that exceeds 99% and approaches 99.7% .

And the waste water leaving the boat has an alkalinity that exceeds Ph=8. With these performances, this system fully meets the environmental conditions for navigation of the international organization IMO (International Maritime Organization), which no other system installed on ships anywhere in the world meets. And the reasons that these systems are insufficient in the total desulfurization of exhaust gases are the following.

Because all existing cationization systems using seawater that contains Ca2SO4 (gypsum) in a high percentage (e.g. in 10 parts of seawater about 8 contain calcium sulfate), i.e. it is already saturated with sulfur, which they intend to remove from the outgoing exhaust gases with cationization and thus drastically limit the possibility of capturing sulfur in the form of sodium sulfate or sulfite.

And for this reason, huge amounts of seawater are required for cationization compared to our system.

To have a picture of the compared sizes for a 56,000 ton ship with an installed 10 MW engine and an outgoing gas volume of about 75,000 tons/h, seawater ionization requires 480 tons/h, while ionization with deionized water coming from the double stage reverse osmosis desalinator only 20 tons/h.

And in addition as mentioned above in row 45 page 1 "they will cause complications in the operation of the unit due to the accumulation of Ca2SO4, Ca2CO3 salts in the scrubber as well as in the venturi tube that is upstream of it", as well as in all the piping with what this entails, as found in implementation of their problematic operation.

An equally important element that must be pointed out is the fact that due to the insufficient desulfurization of the exhaust gases, the rest of the sulfur coming into contact with the sea water creates sulfuric acid and ends up in the water discharged to the sea, which makes it acidic.

And which in turn due to the huge discharge supply and because it is installed at the stern to be diluted by the ship's propeller, in an attempt to meet IMO conditions it in turn corrodes the ship's propeller. In addition, the opening of large channels for the supply and disposal of huge amounts of water per hour, as well as the energy operating costs of oversized pumps necessary for this purpose, have a great impact on the operating and maintenance costs of the units.

In contrast, our proposed system has minimal maintenance costs because we do not use seawater to perform ionization and, moreover, deionized water does not have the corrosive ability of seawater, and the diameter of the intake or discharge pipelines is very small compared to the existing ones desulfurization scrubber units using seawater. The same applies to the power of the pumps, which will be much smaller than those in seawater scrubber units.

Another advantage of our proposed system is that, combined with the operation of the heat recovery unit upstream of the desulfurization unit, it is possible to reduce the temperature of the exhaust gases up to, for example, the temperature of 170 °C and consequently it will stop.

A) greater economic benefit, from heat recovery which translates into fuel reduction due to greater ΔT, as mentioned above on page 2 row 40. B) Much smaller amount of water in tons for ionization (and therefore less energy cost), to lower the temperature instead of ΔT =250-80=170°C the ΔT is equal to ΔT=170-80=90°C and thus less water will evaporate and in addition it will increase the degree of sulfur saturation because the temperatures are lower.

To give an idea of the actual fuel consumption of a ship at sea for 25 days a month equipped with a 10MW diesel engine, the fuel consumption is 25 tons per day

Claims (5)

1. Automatic system for the neutralization of gaseous pollutants from ship chimneys with simultaneous energy recovery is characterized by the fact that the unit consists of submersible pumps of appropriate flow and pressure that feed the tank (1) for the operation of the desalinator (2) with the process of reverse osmosis and the desalinated water to be drained into a tank (3) where an appropriate amount of alkaline solution will be poured according to the control system (25) preferably NaOH with a suitable pH through a dosing pump (4) that supplies from the tank ( 5) of NaOH and then it will feed through a pump (6) with a suitable pressure it will pour-spray in three positions for the cationization of the exhaust gases and which are the first downstream of the exhaust gas inlet in the venturi tube (8) in the pretreatment phase in the second which is the first ionization treatment stage of the scrubber (10) and in the third place which is the second stage where onization of the scrubber, the main exhaust gases will exit to the atmosphere free of S,Ta and the wash water will be collected in a tank (12), and after being properly treated, the oily parts and particles are separated as stock in the tank (13) to be delivered in the selected port, and the wash water is led to the thermal seawater/wash water exchanger (14), and the sea water returns to the sea, and the treated wash water with a lower temperature is led to the tank (3) and to be closed in this way the circuit. All used water is completely renewed every hour. And the reduction of the temperature of the exhaust gases from the chimney is achieved through a thermal exhaust gas/water exchanger (15) in which the exhaust gases are led through a bypass equipped with pneumatic valves, through which the exhaust gas output returns to the previous state. The produced steam is partly led to a steam turbine (16) connected to the electric generator (17) with electricity production and partly to liquefy the fuel oil. 2. Automatic system for neutralizing gaseous pollutants from ship chimneys with simultaneous energy recovery is characterized by the fact that the unit consists of the desalinator with the reverse osmosis process (2) because the salt contained in the seawater must be removed. Otherwise the deposits of this on the elements (scrubber, venture, ejectors, piping) cause over time a blockage and ultimately a drastic reduction in the precipitation of SOx. 3. Automatic system for the neutralization of gaseous pollutants from ship chimneys with simultaneous energy recovery is characterized by the fact that the unit consists of the heat exchanger (15), through which the heat load is assigned to the deionized water that is vaporized and a part of the supply is introduced of the steam to liquefy the fuel oil for the diesel engine, and the remaining supply to a suitable steam turbine (16) connected to the generator (17) for powering the ship. 4. Automatic system for neutralization of gaseous pollutants from ships' chimneys with simultaneous energy recovery is characterized by the fact that the system for recovering energy from exhaust gases for the ship's power supply operates regardless of whether the gaseous pollution neutralization system is in operation or not and vice versa Only in the opposite case, the operation of the gaseous pollutant precipitation system will be burdened, as a much larger amount of water will have to be supplied to reduce the temperature of the exhaust gases due to the high thermal load carried by the exhaust gases, and it will be more costly. 5. Method of neutralizing gaseous pollutants with simultaneous energy recovery is characterized by the fact that by putting the unit into operation, the submersible pumps equipped with each ship automatically operate and transfer seawater from sea level to the tank (1) on deck. From this tank, water is pumped to pass through the desalination system (2) with membranes in a double stage and the residue is discharged into the sea, and the desalinated water is placed in a tank (3) where with a dosing pump (4) NaOH is poured , so that the pH of the aqueous solution is of the desired degree of alkalinity. The dosing pump pumps the caustic soda from a special tank (5), which contains NaOH. From the tank (3) through a pump (6) at a suitable pressure three positions are supplied for the cationization of the exhaust gases and which are the first downstream (7) of the exhaust gas inlet in the venturi tube (8) in the pretreatment phase. In the second which is the first stage (9) treatment-cationization of the scrubber (10). And in the third position (11) which is the second cationization stage of the scrubber. It should also be noted that the alkali solution ejectors shall be properly constructed and operated so that the ejector is perpendicular to the exhaust gas flow and creates a turbulent flow to increase turbulence with the ultimate goal of maximizing surface area. mixing of molecular droplets and molecular gas aggregates, for the effective precipitation of S . The exhaust gases after passing through the venturi tube and then passing through the first and second stage of cationization will exit to the atmosphere at about (70-80)°C, and free of S. The residual wash water together with the particles and the oily and tarry substances will be collected in a tank (12), from where the floating oily and tarry substances are immediately separated and will be stored in another tank (13) for delivery to the selected port. and the wash water, which has a temperature ranging between (80-90) °C, is led to a heat exchanger (sea water/wash water) (14) in which the heat of the wash water is extracted, through sea water at a temperature of about 15° C, so that the recycled water enters the tank (3) at the same temperature. In this way, the demand for desalinated water and consequently the energy consumption becomes minimal as well as for this caustic soda, because the PH of the recycled water is alkaline. Every hour the total water used is completely renewed. The amount of water used is minimal compared to what is available and this has as a consequence the economical operation of the arrangement. Keeping neutralization effectiveness unchanged over time. At the same time, the exhaust gases from the diesel engine entering the heat exchanger (15) (air/water) assign their heat load to the water which is vaporized and the vapor of which in sufficient quantity is first drained into the fuel oil liquefaction system, with which it is equipped all ships that use heavy fuel. With the remaining mass of steam, we feed a steam turbine (16) with a suitable reducer connected to it, with which the generator (17) is paired to power the ship.