NL9401387A - A method of cooling a hot gas stream, for increasing the efficiency of electricity production, and for regulating the cooling process of a synthesis gas stream, such that peaks in electricity demand can be accommodated. - Google Patents

Description

Title: Method for cooling a hot gas stream, for increasing the efficiency of electricity production, and for regulating the cooling process of a synthesis gas stream, so that peaks in electricity demand can be accommodated.

The invention relates to a process for cooling, in particular for cooling by causing an endothermic chemical reaction ("chemical cooling"), a hot gas stream and in particular a synthesis gas stream, to a method of increasing the efficiency of the electricity product using a synthesis gas stream, as well as a method of regulating the cooling process of a synthesis gas stream such that peaks in electricity demand can be accommodated.

It is well known that electricity can be generated with various resources. In particular, the fossil fuels oil, gas and coal are widely used for electricity production. These fossil fuels are burned to drive gas turbines, possibly in combination with steam turbines. The present invention relates to processes in which fossil fuels, but also other hot flammable gases, can be used.

Of the fossil fuels, the use of natural gas for generating electricity is usually preferred. Natural gas burns efficiently in the sense that the overall efficiency for the conversion of natural gas into electricity (efficiency about 55% pp heating value basis) is higher than the overall efficiency for the conversion of other fossil fuels to electricity (efficiency for coal about 43% on the heating value basis). . - The calorific value is the calorific lower value or Lower Heating Value of the gaseous fuel flow to the gas / steam turbine system. - In addition, natural gas produces the least amount of CO2 per generated kWh of electrical power. Furthermore, the use of natural gas, unlike the use of coal, does not lead to the formation of large amounts of fly ash. A disadvantage of natural gas, however, is its uncertain availability at relatively low costs in the long (er) term. In these aspects - low cost and long-term availability - coal is a suitable alternative. However, the direct use of (powder) coal to produce electricity leads to large amounts of carbon dioxide and ash.

In recent years, great interest has become noticeable in processes in which coal, other heavy fossil fuels and other carbon-containing raw materials are not simply burned, but are first gassed. Gasification of the heavy or heavier fuels, whether or not containing carbon, combines the advantages of using natural gas with a large arsenal of available and relatively cheap starting materials. In addition, coal or oil gasification producing fuel gas has an advantage in gas cleaning over coal and oil combustion where only flue gas is generated. More particularly, when gasifying in the upstream gasifier, fuel gas or fuel gas is formed; this in contrast to pulverized coal-fired power plants where the solid pulverized coal serves as fuel. Since the fuel gas is produced at high pressure, cleaning it is easier than cleaning flue gas at low pressure. Due to the higher pressure of fuel gas relative to the flue gas, smaller equipment will suffice for fuel gas cleaning. In addition, in the fuel gas purification, the sulfur components in the form of hydrogen sulfide as elemental sulfur can be removed with a sulfur recovery percentage of 97-99%, while in the flue gas purification, the sulfur component and mainly in the form of sulfur dioxide must be removed as gypsum with a recovery percentage of only 85-90%. The use of gasification technology also results in lower ΝΟχ and fly ash emissions compared to combustion technology.

Gasification plants generally comprise a gasification unit, a cooling section, a gas cleaning section and gas and / or steam turbines.

In a gasification unit, the fossil fuel is partially oxidized with oxygen or an oxygen-containing gas.

Gasification of coal, oil, cracking residues, residues remaining after hydroconversion of atmospheric residues and vacuum residues etc. leads to the formation of so-called synthesis gas. Depending on the starting material, this synthesis gas comprises a complex mixture of hydrogen, carbon monoxide, carbon dioxide, steam, nitrogen, nitrogen oxides, hydrogen sulfide and other compounds formed from the components of the starting material. An example of a gasification process for heavy hydrocarbons is described in European patent application 0 497 425 (Shell); for an example of a coal gasification process, reference is made to European patent application 0 423 401 (The Dow Chemical Company), which will be reverted to below.

Gasification takes place at a relatively high temperature. Oil (residue) gasification typically takes place at a temperature of 800-1500 ° C. Coal is usually gasified at even higher temperatures of 1300-1650 ° C into synthesis gas.

From the gasification zone, the synthesis gas formed is led to a cooling section. This cooling section includes, for example, a synthesis gas cooler (syngas cooler). The syngas cooler is in fact a conventional convective heat boiler, a standard heat exchanger. The synthesis gas is introduced at the top of this cooler and flows from top to bottom.

Heat is exchanged with the water in the boiler, generating steam. The syngas coolers hitherto used usually operate at a temperature of maximum "only" approximately 900 ° C. This temperature is essentially determined by the presence of fly ash in the hot gas phase.

More specifically, a significant amount of fly ash particles are present in the hot synthesis gas. Occasionally, about half of the total amount of ash generated in coal gasification ends up in the hot synthesis gas in the form of fly ash. In the known gasification plants, ash is heated above its melting point. The fly ash particles thus created must be removed from the synthesis gas or solidified before the synthesis gas reaches the syngas cooler; this to avoid the occurrence of blockages or other inconveniences caused by deposition of solid fly ash in the cooler, such as a delayed or insufficient heat transfer between the gas to be cooled and the cooling medium. A suitable way of removing fly ash is to rapidly cool the synthesis gas below the melting point of the fly ash, which in practice means that it must be cooled quickly to ± 900 ° C. In this way, the ash particles do not become sticky, so that the contamination behavior of the pipe surfaces in the syngas cooler is controllable. Incidentally, the solid fly ash particles are only removed from the synthesis gas after the cooling section.

One and the other means that the synthesis gas coming from the gasification zone is in fact too hot to be supplied to the syngas cooler. A precooling step is necessary.

The hot gas is almost always cooled in two steps. The first step, cooling from, for example, 1600 ° C to 900 ° C, can be carried out by quenching with already cooled synthesis gas or water or by cooling with a radiation cooler. Because a radiation cooler is a very expensive device because of the very high requirements for construction and material, it is generally cooled by recycling already cooled synthesis gas or water. When cooling with water, the resulting gas contains a lot of water vapor.

The second cooling step will be performed with the previously mentioned syngas cooler.

At the 250 MWe coal gasification plant in Buggenum, the Netherlands - currently the world's largest integrated coal gasifier - the pre-cooling step is performed by cooling or quenching the hot synthesis gas that has a temperature of 1500-1650 ° C with synthesis gas that has already passed the syngas cooler and that has a temperature of about 250 ° C. In this case, by combining hot and cooled synthesis gas in a ratio of about 1: 1, a synthesis gas stream having a temperature of about 900 ° C is obtained. In this regard, reference can be made to the article by Irwin Stambler, Demkolec 250-MW IGCC sparks gasification projects in Europe, Gas Turbine World: January-February 1993, pages 9-14.

The cooling step with cooled synthesis gas just discussed has a number of drawbacks, the most important of which are now briefly discussed.

First, recirculating cooled synthesis gas requires some mechanical adjustments. For example, a relatively large recirculation compressor is required to return the cooled synthesis gas to the hot gas stream before it reaches the syngas cooler. Another very important mechanical adjustment is related to the fact that an approximately twice the volume of gas must pass through the synthesis gas cooler than the volume of synthesis gas produced. After all, both the hot synthesis gas and the amount of cooled synthesis gas added thereto must be cooled in the syngas cooler. Therefore, a relatively large syngas cooler with a relatively high duty is required for the synthesis gas flow produced by gasification.

When the hot synthesis gas is cooled with cooled synthesis gas that is recycled, there is a considerable loss in the available work potential of the combined gas flows, which the expert refers to as loss of exergy.

As already noted, the cooling section can also be formed by a "radiant heat water tube boiler" in combination with a convective cooler. Such a cooling device is used in Texaco's coal gasification plant and is described in the brochure "Technology available for license from Texaco", Texaco Development Corporation, Artwork & Printing: Image Services, Texaco Inc. Harrison, NY (1989). Due to the high inlet temperature, very high demands are placed on both the construction and the materials of a radiant heat water tube boiler. Therefore, there is a need for a considerably less complicated and less expensive cooling section.

The aforementioned problems are solved, at least greatly reduced, by applying the methods according to the invention.

According to the invention, a hot gas, in particular hot synthesis gas, is cooled using an endothermic reaction. A relatively small amount of a gaseous hydrocarbon and optionally water (preferably in the form of steam) and / or carbon dioxide is injected into the hot (synthesis) gas stream. The gaseous hydrocarbon will react rapidly with the water (see reaction 1) and / or the carbon dioxide (see reaction 2) to substantially carbon monoxide and hydrogen gas under the conditions prevailing in the hot synthesis gas. in fact it is. the reaction between the hydrocarbon and carbon dioxide composed of the so-called "shift reaction" (see reaction 3) and the reaction between hydrocarbon and water (reaction 1) (1) (2) (3)

These reactions are strongly endothermic, as a result of which the temperature of the synthesis gas will drop sharply, depending on the amount of hydrocarbon and possibly steam and / or carbon dioxide introduced. For the sake of completeness, it is noted that a part (sometimes even 40%) of the heat of the hot gas is also used to heat the directly injected reactants to the reaction temperature.

More particularly, the invention relates to a method for chemically cooling a hot gas stream, in particular a hot synthesis gas stream, at a temperature above 900 ° C, in which a gaseous hydrocarbon, and optionally water and / or carbon dioxide, directly in the hot gas flow is conducted.

In a second aspect, the invention relates to a method of increasing the efficiency of electricity production using a synthesis gas stream from a gasification plant, wherein a gaseous hydrocarbon, and optionally water and / or carbon dioxide, is introduced directly into the synthesis gas stream before the product stream is supplied to electricity generating devices.

The process according to the invention is especially advantageous for the chemical cooling of synthesis gas produced by gasification of coal or oil (residues). This gas has a temperature of about 1000-1650 ° C at a pressure between about 25 and 70 bara.

Injection of small amounts of steam or carbon dioxide next to the hydrocarbon stream is only necessary to carry out the process according to the invention if the gas to be cooled contains insufficient of (one of) both compounds to consume sufficient heat in the endothermic reaction.

When only little water and / or carbon dioxide is / are present in the gas to be cooled, the injection of only a gaseous hydrocarbon has only a limited chemical effect. Although the increase in efficiency is limited in this design, an advantage arises in the gas cleaning section by reducing the CO2 co-adsorption.

When relatively much carbon dioxide and steam are present in the hot gas, only injection of a gaseous hydrocarbon is necessary to allow the endothermic reactions to proceed. The resulting synthesis gas in this case still contains significant amounts of CO2 and H2O. In this case, due to the small amount of gas to be injected, the underlying gas cleaning section is subjected to little additional load.

If the hot gas is not sufficiently cooled by the chemical reaction alone, depending on the respective process conditions, it can be further cooled by physical cooling by either recirculation of gas cooled in the cooling section or by direct injection of additional gaseous hydrocarbon and / or water and / or carbon dioxide. Since extra water has a negative effect on the efficiency and since extra carbon dioxide impairs the synthesis gas mixture, only extra hydrocarbon is preferably injected. In the manner just described, a two-part refrigeration process is formed in which a chemical quench is initially performed and a physical quench is used in the second instance.

The hot gas composition has relatively little influence on the effect of the endothermic reaction to be carried out according to the method of the invention. The temperature drop is due to the dissipation of sensible heat. At the temperatures of the hot gas, the heat capacities of the different hot (synthesis) gas components are approximately equal. Only the presence of water vapor and carbon dioxide in the hot gas flow influence the process to some extent, because these gases participate in the endothermic, cooling reaction.

Electricity is generated in a gasification installation with the steam generated in the syngas cooler and - for the most part - in the gas and / or steam turbines.

Steam is generated in the syngas cooler. This steam can be used to generate electricity with an energetic efficiency of about 40%.

The gas cooled in the syngas cooler, after any usual gas treatment steps, such as solid separation, washing, desulphurisation, etc., is burned in a gas turbine, generating electricity. An attractive method of generating electricity uses a combination of the gas turbine just mentioned and a steam turbine: the so-called STEG unit. The gas mixture is burned in such a CCGT unit. The combustion gases are then allowed to expand in the gas turbine, whereby electricity is generated. The hot exhaust gas from the gas turbine is then used to produce high-pressure steam. This steam is then expanded in the steam turbine, which also produces electricity. The total energy efficiency of a STEG unit, a device known from the prior art, is normally around 55% based on the calorific value.

The methods of the invention have the following advantages in terms of efficiency.

A conversion of a gaseous hydrocarbon to synthesis gas takes place. The synthesis gas gives a higher efficiency in electricity production in a gas turbine than the gaseous hydrocarbon output.

A second advantage lies in that less steam is produced in the cooling section. The total gas flow through the cooling section is reduced using the cooling method according to the invention compared to the known physical cooling method as it is used, for example, in the gasification installation in Buggenum. The overall efficiency for electricity production from steam (40% on an enthalpy basis) is much lower than the overall efficiency for electricity production from synthesis gas (> 50% on a calorific value basis).

A third advantage arises from the fact that the chemical exergy loss in the quench by means of a chemical reaction is lower than with a physical quench. The amount of cold gas supplied is much lower, so that the loss of physical exergy is greatly reduced. The endothermic reaction takes place at the bulk temperature of the gas, so that only a limited loss of exergy occurs due to the progress of the chemical reactions during chemical cooling.

Due to the endothermic reaction, the heat released during the cooling of the hot synthesis gas is, as it were, stored in the form of chemical energy. The products formed are products which can already be detected in the hot gas.

Electricity can be obtained with a higher overall efficiency by converting physical energy into chemical energy. In fact, the electricity producing efficiency from the combined synthesis gas / gaseous hydrocarbon stream is higher than the total efficiency of the synthesis gas stream and the hydrocarbon stream when fed separately to the electricity-supplying gas turbine or CCGT unit. In other words, the losses are lower in chemical cooling than in cooling with recycled synthesis gas. This increases the efficiency for electricity production. This increase in efficiency is in the order of 0.5-1.5%, for example 0.8%, which represents a very significant progress on a calorific value basis.

In addition, as stated, the gas flow through the syngas cooler decreases. After all, much less gaseous hydrocarbon and optionally water or steam and / or carbon dioxide has to be supplied in volume than that cooled synthesis gas must be mixed in order to achieve a desired synthesis gas temperature. All this leads to reduced investment costs. On the one hand, a smaller syngas cooler suffices, on the other hand, a smaller or ideally no recirculation compressor is required for the return of cooled synthesis gas. When natural gas is used as the gaseous hydrocarbon injected into synthesis gas according to the invention, a syngas cooler having a capacity of 70-80% of that of the conventional syngas cooler will suffice.

As the gas flow through the syngas cooler decreases, steam production also decreases.

Incidentally, from the above-mentioned European patent application 0 423 401 a method is known in which synthesis gas is cooled by allowing endothermic reactions to take place in a (second) reactor which is coupled to a coal gasification unit. in this patent application, in which the generation of electricity is not primarily intended, if not even mentioned, in the second reactor a slurry of a particulate hydrocarbon material in a liquid carrier is introduced into the synthesis gas product prepared by gasification. The particulate hydrocarbon material includes heavy hydrocarbon compounds such as lignite, bituminous coal and sub-bituminous coal. Furthermore, coke from coal, coal tar, petroleum coke, as well as coal-like material obtained from shale oil, tar sand, pitch, concentrated sewage sludge, rubber, etc. can be added. Water is preferably used as the liquid phase. This heavy "cooling material" results in the formation of relatively many different reaction products compared to the products formed from the gaseous hydrocarbons and water and / or carbon dioxide, the reactants in the processes of the invention. This means that additional gas cleaning steps or at least more extensive gas cleaning steps are required. Apart from the nature of the material supplied and the drawbacks associated therewith, the method of EP-A-0 423 401 requires very complicated equipment for introducing the "cooling material".

Using the method according to the invention, essentially no foreign components enter the synthesis gas, so that it is not necessary to make substantial mechanical adjustments in the gas cleaning section.

The hydrocarbons or mixture of hydrocarbons introduced into the hot synthesis gas according to the present invention are required to react endothermically with water molecules and / or carbon dioxide molecules, with essentially no reactions with other components present in the synthesis gas. Suitable hydrocarbons meeting these criteria are Οχ.4 alkanes, as well as mixtures of such alkanes. Higher hydrocarbons may also be used. Natural gas, refinery gas, and / or LPG are preferably used as the hydrocarbon component. The term refinery gas refers to the light hydrocarbon fractions formed as a by-product of oil or oil residues cracking, distilling, platforming, etc. Light cracking products of other organic material such as biomass, wood and waste can also be used. Since gas purification plants are present in the process line of a gasification plant, it is not a problem when slightly contaminated gaseous hydrocarbons, such as crude, either "acid" natural gas or refinery gas, are used.

Depending on the amount of water and carbon dioxide already present in the hot synthesis gas, additional water may or may not have to be injected in addition to the hydrocarbon stream, usually in the form of steam, and / or carbon dioxide. In fact, the endothermic reaction per carbon atom of the hydrocarbon compound requires a water molecule or a carbon dioxide molecule. However, the ratio of gaseous hydrocarbon to water and / or carbon dioxide is not critical. The addition of an excess of gaseous hydrocarbon or an excess of water and / or carbon dioxide will provide physical cooling. Since the presence of water in the synthesis gas can lead to condensation in later steps, which gives energetic disadvantages, and since the presence of an excess of CO2 burdens the underlying gas cleaning and electricity generation, an excess of hydrocarbon will preferably be injected.

In a preferred embodiment of the method according to the invention, a synthesis gas is produced in which as little CO2 as possible is present. This embodiment can be accomplished by adding so much hydrocarbon gas that substantially all of the carbon dioxide is consumed in the reaction with hydrocarbon.

Overall, coal gas from a dry gasification plant contains approximately 2% CO2 and 3% h 2 O. in a wet gasification process, these values are considerably higher, for example 11% CO2 and 13% H2O. The person skilled in the art can determine the composition of the gas to be cooled in a relatively simple manner according to known techniques. On the basis of this data, he can determine the supply of the reactants to be injected, depending on the gaseous hydrocarbon to be used and the water and / or carbon dioxide gas to be injected. It is usually sufficient to introduce about 5-10% methane directly into the hot gas stream.

The reaction product of the endothermic reaction used to cool the synthesis gas stream consists largely of carbon monoxide and hydrogen gas. This product mixture enriches the synthesis gas flow which leads to a higher efficiency in the STEG unit.

Incidentally, the advantages of the present invention are also obtained, albeit to a slightly lesser extent, if a chemical cooling step is first carried out by direct injection of a gaseous hydrocarbon into the synthesis gas to, for example, 1200 ° C, which cooling step can be followed by a synthesis gas quench, a cooling step in which cooled synthesis gas is recycled. For the second cooling step, only a relatively small part of the synthesis gas now needs to be recycled. In fact, the advantages in the chemical quench portion are similar to the embodiments already described. In addition, the current through the syngas cooler may even decrease. However, the overall efficiency is less compared to the separate generation of energy from the synthesis gas flow on the one hand and the hydrocarbon gas flow on the other.

One of the reasons for carrying out the two-step cooling may be that the gaseous hydrocarbon to be used for chemical cooling will react effectively with water and / or carbon dioxide molecules only up to a certain minimum temperature. It may be that, depending on the conditions in the hot synthesis gas, the endothermic reaction proceeds above, for example, 1200 ° C with a high conversion of about 80% and at a temperature of, for example, 900 ° C has only a low equilibrium conversion of only 30%. More specifically, at lower temperature, the endothermic reaction will shift to the hydrocarbon side. Moreover, the reaction rate also decreases with temperature. This means that, depending on the composition of the hot gas and the reactants to be injected and the other process conditions, there is a minimum temperature below which the chemical cooling reaction is negligible and only physical cooling takes place. In general, the relatively low temperature and the relatively high pressure, thermodynamic and reaction kinetics, are less suitable for the chemical reaction in question.

The principles underlying the present invention can be elaborated in accordance with a further aspect of the invention.

Namely, the invention further relates to a method for regulating the cooling process of a synthesis gas stream in such a way that peaks in the electricity demand can be absorbed, wherein an increased electricity production is obtained because the cooling step of the synthesis gas is carried out, depending on the increased energy demand, by injecting a gaseous hydrocarbon and optionally water and / or carbon dioxide stream in combination with the recirculation of already cooled synthesis gas or with the physical cooling with a gaseous hydrocarbon, water or carbon dioxide stream.

This regulation method can be described in more detail as follows. At a normal base load of the gas fired power plant, cooling can be performed using the chemical cooling method of the invention in combination with a second cooling step using recycle gas. According to the invention, if the demand for electricity increases at a certain time of the day, it is possible to switch from recirculation cooling in the second cooling step to a cooling process in which a cold gaseous hydrocarbon stream is injected directly into the synthesis gas stream. Thus, in the second cooling step, use is made of a physical cooling with a gaseous hydrocarbon stream. Switching from one physical cooling process to another can produce a peak / base load ratio of up to 1: 1.6 using methane as a gaseous hydrocarbon. All this makes it suitable to apply this method according to the invention for a flexible day / night power control of a power plant.

A very suitable coolant with which the chemical and physical cooling can be carried out is an unpurified hydrocarbon gas stream, for example an acidic natural gas stream or an unpurified refinery gas stream.

if an even more flexible regulation for peaks in electricity demand is required, while the gasification unit is nevertheless continuously run at full capacity, cooling can initially be carried out conventionally with cooled recycle synthesis gas. Depending on the electricity demand, at some point (part of) the recirculation cooling can then be replaced by the chemical cooling method according to the invention, after which the method for regulating the cooling process according to the invention can be further carried out. When switching from conventional cooling with recycled cooled synthesis gas to a chemical quench and injection of methane gas for the additional physical quenching, a peak / load ratio of up to 1: 1.8 can be achieved.

The present invention will now be further elucidated by means of the following examples in which a comparison is made between three cooling methods.

Example 1

In this example, it is shown that the use of the chemical cooling of gas from a gasification installation by injection of methane and steam in combination with physical cooling with recirculation gas according to the invention leads to a higher efficiency in electricity generation and a smaller syngas cooler is required compared to prior art separate generation of electricity.

A gaseous methane flow of 0.047 kmol / s and a temperature of 25 ° C together with an amount of steam of 0.047 kmol / s and a temperature of 250 ° C was injected into a coal gas flow of 1 kmol / s and a temperature of 1614 ° C . The coal gas stream had the following composition: 27.8 mol% hydrogen, 63.1 mol% carbon monoxide, 1.6 mol% carbon dioxide, 5.1 mol% nitrogen, 0.3 mol% hydrogen sulfide and 2.1 mole% water. The pressure at the injection site was about 27 bara.

After injection, a gas flow of 1.18 kmol / s with a temperature of 1200 ° C resulted, which was 34.2 mol% hydrogen, 57.0 mol% carbon monoxide, 1.4 mol% carbon dioxide, 4.4 mol. % nitrogen, 0.3 mole% hydrogen sulfide, 2.2 mole% water and 0.5 mole% methane.

This gas stream was further cooled to 900 ° C by admixture of 0.58 kmol / s coal gas cooled in the synthesis gas cooler and a temperature of 247 ° C, which of course had the same composition as the gas described in the previous paragraph. A gas flow of 1.76 kmol / s was generated.

This gas stream was cooled to 235 ° C in the syngas cooler to generate 0.72 kmol / s steam at 250 ° C and 27 bar.

This steam was converted into electricity in a steam turbine with an exergetic efficiency of 90%.

A gas flow of 0.58 kmol / s was recycled to the physical quench admixture site after recompression.

The 1.18 kmol / s product gas stream was fed to a STEG unit. This gas flow was converted into electricity in the STEG unit with an efficiency of 57.51% on a calorific value basis.

The net electricity production in the steam turbine and the STEG unit was 180.5 MW.

For comparison, the methane and coal gas streams used in accordance with the invention were also used separately for the production of prior art electricity.

To this end, the methane flow of 0.047 kmol / s and a temperature of 25 ° C was burned in the STEG unit, generating 20.9 MWe of electricity with an efficiency of 55.97% on calorific value.

The coal gas stream (1 kmol / s; 27 bara; 1614 ° C) was now brought to a temperature of 900 ° C (2.2 kmol / s) completely with recycled cooled gas (1.20 kmol / s; 247 ° C) . This gas stream was cooled to 235 ° C in a syngas cooler to generate 0.91 kmol / s steam at 250 ° C and 27 bar. A gas flow of 1.2 kmol / s was recycled for physical quenching. The product flow of 1.0 kmol / s was fed to the STEG unit.

A net 157.8 MWe of electricity was thus produced from the coal gas flow, with a yield of 57.47% on a calorific value basis.

In total, with separate generation, electricity was produced in a net capacity of 178.8 MW. This means that the increase in efficiency by applying the method according to the invention is 0.6% on a calorific value basis.

Application of the chemical cooling step results in a 20% reduction in the gas flow through the syngas cooler as well as its duty.

Example 2

In this example, it is shown that the use of chemical cooling by injection of methane and steam in combination with physical cooling by injection of a hydrocarbon according to the invention results in a higher efficiency in electricity generation and a smaller syngas cooler is required in comparison with separate generation of prior art electricity.

The procedure as described in Example 1 was repeated with the change that now the physical cooling step was not carried out with recycled cooled coal gas but with a flow of 0.24 kmol / s methane at 25 ° C. Thus, a gas stream at a temperature of 900 ° C was obtained from the following composition: 28.5 mol% hydrogen, 47.6 mol% carbon monoxide, 1.2 mol% carbon dioxide, 3.6 mol% nitrogen, 0 .2 mole% hydrogen sulfide, 1.7 mole% water and 17.0 mole% methane.

Subsequently, this gas stream in the syngas cooler was cooled to a temperature of 235 ° C, generating 0.68 kmol / s steam of 27 bar and 250 ° C. The product gas was fed to a STEG unit, where it was converted into electricity with a yield of 57.15% on calorific value.

Net 286.7 MWe of electricity was generated in the steam turbine and the STEG unit.

Also now it has been compared to a process in which the coal gas stream and the methane gas stream were used separately for the production of electricity.

The gaseous methane stream of 0.28 kmol / s and a temperature of 25 ° C was used in an STEG unit for the production of electricity. The conversion to electricity took place with a yield of 55.97% on a calorific value basis, which yielded 126.5 MWe of electricity.

In accordance with Example 1, the coal gas flow provided 157.8 MW

A total of 284.3 MWe of electricity was therefore produced with separate generation.

The yield increase when using the method according to the invention is therefore 0.5% on a calorific value basis.

Example 3

In this example, it is shown that the use of chemical cooling by injection of methane and carbon dioxide in combination with physical cooling with recirculation gas according to the invention leads to a higher efficiency in electricity generation compared to separate generation of electricity according to the prior art.

A gaseous methane stream of 0.040 kmol / s and a temperature of 25 ° C together with an amount of carbon dioxide of 0.040 kmol / s and a temperature of 25 ° C was injected into a coal gas stream of 1 kmol / s and a temperature of 1614 ° C . The coal gas stream contained 27.8 mol% hydrogen, 63.1 mol% carbon monoxide, 1.6 mol% carbon dioxide, 5.1 mol% nitrogen, 0.3 mol% dihydrogen sulfide and 2.1 mol% water . The pressure of the gas at the injection point was about 27 bara. After injection, a gas flow of 1.15 kmol / s with a temperature of 1200 ° C was generated, which contained 30.2 mol% hydrogen, 61.1 mol% carbon monoxide, 1.6 mol% carbon dioxide, 4.4 mol. % nitrogen, 0.3 mole% dihydrogen sulfide, 2.0 mole% water and 0.4 mole% methane.

This gas stream was cooled to 900 ° C by physical admixture of a recirculation stream of already cooled gas of the same composition of 0.57 kmol / s and a temperature of 247 ° C. This resulted in a gas flow of 1.72 kmol / s with an unchanged composition. Subsequently further cooling to 235eC took place in a syngas cooler generating 0.71 kmol / s steam at 250 ° C and 27 bar.

A gas flow of 0.57 kmol / s was recycled to the physical quenching point after recompression.

The product gas flow was 1.15 kmol / s. Application of this gas flow for electricity production in a CCGT unit with a yield of 57.49% on heating value, as well as the conversion of the steam produced to electricity in a steam turbine with an exergetic efficiency of 90%, resulted in a net electricity production of 178.0 MW.

For comparison, a process was conducted in which the natural gas and coal gas streams used above were used separately for the production of prior art electricity.

A gaseous methane stream of 0.040 kmol / s and a temperature of 25 ° C was burned in an STEG unit for the production of electricity. The conversion to electricity took place with an efficiency of 55.97% on a calorific value basis, resulting in an electricity production of 18.0 MWe.

As already described in previous examples, use of the coal gas flow according to the conventional method led to an electricity production of 157.8 MW.

In total, a power of 175.8 MWe is generated with separate generation. This means that the profitability of the chemical quench has increased by 0.8% on a calorific value basis.

Example 4 in this example is shown that the use of chemical cooling by injection of methane only leads to the production of synthesis gas with only a very small amount of carbon dioxide and water.

A gaseous methane stream of 0.09 kmol / s and a temperature of 25 ° C was injected into a coal gas stream of 1 kmol / s and a temperature of 1614 ° C. The coal gas stream contained 27.8 mol% hydrogen, 63.1 mol% carbon monoxide, 1.6 mol% carbon dioxide, 5.1 mol% nitrogen, 0.3 mol% dihydrogen sulfide and 2.1 mol% water . The pressure at the injection point was about 27 bara. After injection, a gas flow of 1.15 kmol / s with a temperature of 1200 ° C was generated, which contained 31.6 mol% hydrogen, 58.7 mol% carbon monoxide, 0.1 mol% carbon dioxide, 4.4 mol. % nitrogen, 0.3 mole% dihydrogen sulfide, 0.2 mole% water and 4.7 mole% methane.

After further cooling the synthesis gas to 235 ° C, the gas was cleaned in a gas cleaning section. The very low CO2 content gave the advantage that co-absorption of CO2 was no longer a problem with the absorption of H 2 S using sulpholol. As a result, the required capacity of the gas cleaning equipment is lower, which results in an economic advantage.

Example 5 in this example is shown that the use of chemical cooling by injecting only methane into a coal gas stream from a wet gasification plant in combination with physical cooling with recirculation gas according to the invention leads to a higher efficiency in electricity generation than in separate generation of electricity according to the state of the art.

A gaseous methane stream of 0.032 kmol / s and a temperature of 25 ° C was injected into a coal gas stream of 1 kmol / s and a temperature of 1474 ° C. The coal gas stream contained 29.4 mol% hydrogen, 43.5 mol% carbon monoxide, 11.1 mol% carbon dioxide, 2.0 mol% nitrogen, 0.2 mol% dihydrogen sulfide and 13.8 mol% water . The pressure at the injection point was about 40 bara. After injection, a gas flow of 1.10 kmol / s with a temperature of 1200 ° C was generated, which contained 32.4 mol% hydrogen, 45.7 mol% carbon monoxide, 7.0 mol% carbon dioxide, 1.8 mol. % nitrogen, 0.1 mole% hydrogen sulfide, 12.9 mole% water and 0.1 mole% methane. This gas stream was cooled to 900 ° C by physical admixture of already cooled gaseous recirculation stream with the same composition of 0.54 kmol / s and a temperature of 238 ° C. This produced a gas flow of 1.64 kmol / s with an unchanged composition. Subsequently further cooling to 235 ° C took place in a syngas cooler generating 0.71 kmol / s steam at 250 ° C bar and 27 bar. A gas stream of 0.54 kmol / s was fed to the hot gas stream after recompression for physical quenching. The product gas flow was 1.10 kmol / s. Application of this gas flow for electricity production in a CCGT unit with a yield of 58.50% on a heating value basis, as well as the conversion of the net steam produced into electricity in a steam turbine with an exergetic efficiency of 90%, resulted in a net electricity production of 147.1 MW.

As a reference again a method was used in which the above-used methane and coal gas streams were used separately for the production of electricity according to the prior art.

A gaseous methane stream of 0.032 kmol / s and a temperature of 25 ° C was burned in an STEG unit for the production of electricity. The conversion to electricity took place with an efficiency of 55.97% on a heating value basis, resulting in an electricity production of 14.5 MWe.

A coal gas flow of 1 kmol / s, a pressure of 40 bar and a temperature of 1614 ° C, which contains 29.4 mol% hydrogen, 43.5 mol% carbon monoxide, 11.1 mol% carbon dioxide, 2.0 mol % nitrogen, 0.2 mole% hydrogen sulfide and 13.8 mole% water, was cooled by mixing with a gas stream having the same composition of 0.94 kmol / s and a temperature of 243 ° C. After the quench, the gas flow had 1.94 kmol / s and a temperature of 900 ° C. Subsequently, further cooling to 235 ° C took place in a syngas cooler generating 0.86 kmol / s steam at 250 ° C and 27 bar. A gas flow of 0.94 kmol / s was recycled after recompression for the physical cooling step.

The product gas flow was 1.0 kmol / s. The use of this gas flow for electricity production in a STEG unit with an overall efficiency of 58.77% on a calorific value basis, as well as the net steam produced in a steam turbine with an exergetic efficiency of 90%, resulted in a net electricity production of 131.1 MWe . In total, therefore, a power of 145.6 MWe is generated with separate generation. This means that the profitability of the chemical quench has increased by 0.7% on a calorific value basis.

Claims (8)

Method for the chemical cooling of a hot gas stream, in particular a hot synthesis gas stream, with a temperature above 900 ° C, characterized in that at least one gaseous hydrocarbon, and optionally water and / or carbon dioxide, directly in the hot gas stream is being fed. 2. A method for increasing the efficiency of the electricity production using a synthesis gas stream from a gasification device, characterized in that at least one gaseous hydrocarbon, and optionally water and / or carbon dioxide, is (are) fed directly into the synthesis gas stream, before the gas flow is supplied to electricity generating devices. 3. A method of producing electric current using a synthesis gas stream, characterized in that peaks in the electricity demand can be absorbed and an increased efficiency of the electricity production is obtained by regulating the synthesis gas, depending on the increased energy demand is cooled by injecting at least one gaseous hydrocarbon and optionally water and / or carbon dioxide stream in combination with the recirculation of already cooled synthesis gas or by physical cooling with a gaseous hydrocarbon, water or carbon dioxide stream. Process according to any one of the preceding claims, characterized in that an alkane with 1-4 carbon atoms or a mixture of such alkanes is used as the gaseous hydrocarbon. A method according to any one of the preceding claims, characterized in that natural gas or refinery gas is used as the gaseous hydrocarbon. A method according to any one of the preceding claims, characterized in that the chemical and physical cooling is carried out with a crude hydrocarbon gas stream. Process according to any one of the preceding claims, characterized in that a synthesis gas is obtained with a very low content of carbon dioxide gas. Use of per se known calculation models for generating a flowchart for setting and determining the process parameters for the methods of any one of claims 1-6.