DE19507098A1 - Prodn. of city gas contg. methane - Google Patents

Abstract

Prodn. of city gas contg. 20-50 vol.% methane comprises gasifying a solid, liquid or gaseous fuel by partial oxidn. and producing a gasified gas, which is de-dusted, cooled and desulphurised to produce a gas mixt. consisting of at least 90 vol.% H2,CO and CO2. The novelty is that a synthesis gas is produced, whose concns. of H2,CO and CO2 give the stoichiometric ratio S=(H2-CO2):(CO+CO2)= 1.9-2.3. A part of the synthesis gas is fed through a saturation zone, in which it is contacted with water at 100 deg C and is thus enriched with water vapour. The gas leaving the zone is catalytically converted at 250-550 deg C and the converted gas is divided into a 1st partial stream of 50-95% of converted synthesis gas and a residual stream. The 1st partial stream is fed through a catalytic methane synthesis operating at 250-500 deg C. Part of the methane-contg. gas leaving the methane synthesis is fed together with the residual stream through a cooling zone, in which the gas mixt. is sprayed with water, which is withdrawn from the saturation zone. The methane-contg. gas mixt. withdrawn from the cooling zone is dried.

Description

The invention relates to a method for generating Town gas with a methane content of 20 to 50 vol .-%, whereby a solid, liquid or gaseous fuel gasified by partial oxidation and a crude Gasification gas generated, which is dedusted, cooled and desulfurized and a desulfurized gas mixture is generated, which consists of at least 90 vol .-% of the gas components H₂, CO and CO₂ exists.

In Ullmann’s Encyclopedia of Industrial Chemistry, 5th edition, volume A 12, pages 204 to 233, is detailed described how to make solid or liquid Fuels, e.g. B. coal or heavy oil, by various Gasification process by means of partial oxidation u. a. Can produce syngas or town gas. Show city gases usually calorific values of at least 4 kWh / Nm³, they According to international standards, a maximum of 10 vol .-% CO and preferably the content of CO should be below 3 vol .-% are. The calorific value of purified synthesis gases is usually around 3 kWh / Nm³.

To generate a city gas from a synthesis gas, must part of the synthesis gas methane to be generated Increase calorific value. The conversion of synthesis gas into Methane in the presence of catalysts is known and z. B. in DE-C-24 36 297 and in US-A-4 061 475.

The object of the invention is based on a gas mixture which consists of at least 90% by volume Gas components H₂, CO and CO₂ exists and as syngas designate, city gas in an inexpensive way produce. It should be possible from the synthesis gas at the same time also methanol or other products, e.g. B.  Hydrocarbons, to make the flexibility of the Improve overall process.

According to the invention, the task at the beginning Process solved by generating a synthesis gas whose concentrations of the gas components H₂, CO and CO₂ a stoichiometric number

S = (H₂-CO₂): (CO + CO₂) = 1.9 to 2.3

reveal that at least part of the synthesis gas through a saturation zone, in which the Synthesis gas in contact with water of at least 100 ° C brings and the synthesis gas with water vapor enriches that one comes from the saturation zone Synthesis gas catalytically converted at 250 to 550 ° C that the converted synthesis gas into a first partial stream from 50 to 95% of the converted synthesis gas and one Residual current divides that the first partial flow through a catalytic methane synthesis leads, which in Temperature range of 250 to 500 ° C works that one at least part of that coming from methane synthesis methane-containing gas together with the residual stream through a Cooling zone passes in which the gas mixture with water sprinkles, which is withdrawn from the saturation zone, and that the methane-containing withdrawn from the cooling zone Gas mixture dries. To calculate the stoichiometric number are in the above formula known to those skilled in the art the concentrations of the gas components in mol% to use.

Because the content of hydrogen in the gasification gas is too low is a must before or after desulfurization Conversion done. The conversion will catalytically in a known manner CO + H₂O to CO₂ + H₂ implemented, details are in Ullmann's encyclopedia of technical chemistry, 4th edition, volume 14, pages 422 bis  425. Instead of the conversion you can also Add hydrogen from an external source, as in U.S. Patent 5,310,506.

In the method of the invention one can of solid Fuels such as coal or lignite that go out in lumpy, granular or dusty form gasified. You can also use liquid or gaseous fuels such as Crude oil, heavy oil, residual oils or bitumen, also with Water can be emulsified, as well as use natural gas. For all of these substances are known gasification processes as well as the dedusting, cooling and desulfurization of the generated gasification gas to along with that as well known conversion of a synthesis gas with S = 1.9 to 2.3 and preferably 2.0 to 2.2. For this Synthesis gas can be copper-containing in a known manner Catalysts at temperatures in the range of 200 to 300 ° C and pressures of 40 to 120 bar methanol are generated. The The same synthesis gas can also be used in one Fischer-Tropsch synthesis for the generation of Hydrocarbons are used.

For the production of town gas from the synthesis gas First of all, the one intended for city gas production Converted synthesis gas. Then a partial flow of the converted synthesis gas through a methane synthesis performed with known catalysts, e.g. B. on the Base of nickel, works. A variant of the Methane synthesis consists in that a partial stream of withdrawn from the methane synthesis methane-containing gas in the Cycle leads back to methane synthesis. This Circulation gas dampens the temperature rise through the Exothermic reactions leading to methane formation

CO + 3 H₂ = CH₄ + H₂O and

CO₂ + 4 H₂ = CH₄ + 2 H₂O.

If you partially include the methane synthesis in the cycle operated product gas, you can do the synthesis yourself perform adiabatically, which is favorable in terms of apparatus.

Preferably, that coming from methane synthesis methane-containing gas with the production of water vapor indirectly chilled. Alternatively, you can also use indirect cooling in integrate the synthesis and thereby generate water vapor. The water vapor generated in this way is a additional resource that is used in the production of city gas as a product.

In the method of the invention this is for the City gas generation provided synthesis gas preferably to 100% and not just part of it through conversion guided. In doing so, you generate a converted gas with only a low residual CO content of less than 5% by volume. Therefore, you can then the partial flow of converted gas, which is obtained through methane synthesis leads, keep relatively small and so the effort for the Make methane synthesis inexpensive. Still arises when combining the product gas of the methane synthesis with the Rest of the converted, non-methanized gas Gas mixture with the desired low CO content. For the Methane synthesis is also beneficial in that converted gas is processed. Therefore one can z. B. work with a reduced circuit fan, because the Heat tone in the methane synthesis by the previous one Conversion is reduced, making only a relative one small amount of cycle gas is required. It also has It has been shown that the distribution of energy flows over the Circulating water between the cooling zone and the Saturation zone and on the generation of water vapor is cheap and energy losses are kept low.  

The drawing shows a flow diagram of the process in schematic representation.

Solid, liquid or gaseous fuel, e.g. B. coal or heavy oil, is given up through line ( 1 ) of gasification ( 2 ), which is fed through line ( 3 ) technically pure oxygen and through line ( 4 ) water vapor. The gasification by partial oxidation generates a hot raw gas, which is fed to a dedusting and cooling ( 6 ) in line ( 5 ). This is followed by a catalytic conversion ( 7 ) and a desulfurization ( 8 ). The details of these process steps are known to those skilled in the art, and numerous variations are possible. So z. B. the gasification of fine-grained coal in the circulating fluidized bed and the desulfurization at temperatures below 0 ° C with a physically active detergent, for. As methanol, are carried out, not only sulfur compounds, but also part of the CO₂ are removed from the gas mixture. The conversion ( 7 ) can be replaced by adding hydrogen from an external source.

A synthesis gas with a stoichiometric number S = 1.9 to 2.3 and preferably 2.0 to 2.2 is available in line ( 10 ). This synthesis gas usually has a temperature in the range from 0 to 200 ° C. and a pressure in the range from 5 to 100 bar due to previous compression in the aforementioned treatment stages.

A partial flow of the synthesis gas can be led through the open valve ( 11 a) and the line ( 11 ) to a methanol synthesis plant ( 12 ). Plants of this type are known and z. B. in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, volume A 16, pages 467 to 475. The methanol produced is drawn off in line ( 13 ) and a residual gas (“purge gas”) which contains hydrogen, carbon oxides and methane is drawn off in line ( 14 ). This residual gas, the amount of which is small, is mixed with the gas in line ( 10 ). As a result, the stoichiometric number in the synthesis gas of line ( 10 ) is practically unchanged.

At the same time, or alternatively, one can (11 b) (11 c) supplying a portion of the synthesis gas in line (10) through the opened valve and the line of a plant (12 a) for the Fischer-Tropsch synthesis. Details of such systems are described in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, volume A 7, pages 203 to 217.

In line ( 15 ), the remaining synthesis gas is fed to a saturator ( 16 ), to which water at a temperature of at least 100 ° C. is fed through line ( 17 ). The synthesis gas is enriched with water vapor in the saturator ( 16 ); additional water vapor can be mixed into the synthesis gas through line ( 18 ).

Synthesis gas, which is completely or largely saturated with water vapor, leaves the saturator ( 16 ) in line ( 19 ) and flows for heating first through an indirect heat exchanger ( 20 ) before passing through line ( 21 ) at a temperature of about 250 up to 350 ° C in the catalytic conversion ( 22 ). The conversion works in the temperature range of 250 to 550 ° C, at a pressure in the range of 10 to 100 bar and preferably 20 to 60 bar with a catalyst such. B. iron-based. Deviating from the representation of the drawing, the conversion ( 22 ) can also be designed in several stages.

The converted synthesis gas leaves the conversion ( 22 ) in the line ( 24 ), gives off heat in the heat exchanger ( 20 ) and flows on in the line ( 24 a). Then the synthesis gas is divided into a first partial flow, which is first led through line ( 25 ) to the heat exchanger ( 26 ). This first partial flow comprises 50 to 95% of the amount of gas which has left the conversion ( 22 ) in the line ( 24 ). The remaining part of the converted synthesis gas, which is referred to here as the residual current, flows out in line ( 27 ).

Converted synthesis gas cooled in the heat exchanger ( 26 ) flows in line ( 28 ) together with recycle gas from line ( 29 ) to a methane synthesis ( 30 ). In methane synthesis ( 30 ), CO and CO₂ are converted to methane with hydrogen. The methane synthesis works at temperatures in the range from 250 to 500 ° C. and pressures in the range from 10 to 100 bar and preferably 20 to 60 bar. Suitable catalysts can e.g. B. contain nickel as the main component.

In the process shown in the drawing, the methane synthesis ( 30 ) is operated adiabatically, ie there is no indirect cooling of the catalyst. The recirculated product gas from line ( 29 ), which is returned to the methane synthesis under the action of the compressor ( 29 a), dampens the temperature rise caused by the exothermic methanation reactions.

The methane-rich gas mixture, which leaves the methane synthesis ( 30 ) in line ( 31 ), is first passed through an indirect heat exchanger ( 32 ) which is connected to a collecting container ( 33 ) for the water vapor generated. Boiler feed water is fed to the container ( 33 ) through the line ( 34 ), water passes through the down line ( 35 ) to the heat exchanger ( 32 ) and a water vapor / water mixture is fed back into the container ( 33 ) in line ( 36 ) . Water vapor formed, which is saturated steam, is drawn off in line ( 37 ) and a part of it, usually at most 10%, can be fed through line ( 18 ) into the synthesis gas of line ( 19 ). Excess steam, which is a valuable product, is available for further use in line ( 37 a).

A partial stream of the methane-rich cycle gas is branched off in line ( 40 ) and the gas is combined with the residual stream of line ( 27 ). The gas mixture is first passed through an indirect heat exchanger ( 41 ) for cooling and then fed to a sprinkler cooler ( 43 ) through line ( 42 ). A first stream of cooled circulating water is fed to the cooler through line ( 44 ) and a second stream of cooled circulating water is fed through line ( 45 ). While the water of the two streams trickles down over packing layers or contact trays, the gas in the sprinkler cooler ( 43 ) flows upwards in direct contact with the circulating water. Part of the water vapor content of the gas mixture is condensed and drawn off from the sump of the cooler ( 43 ) together with circulating water in the line ( 46 ).

Cooled, methane-containing product gas, which still contains water vapor, leaves the cooler ( 43 ) in the line ( 47 ), flows through a further indirect cooler ( 48 ) and is then passed through the line ( 49 ) to a gas dryer ( 50 ). Drying is carried out in a manner known per se using glycol, water taken up being released again by heating the glycol. The gas in line ( 51 ) can be used as town gas.

The circuit water withdrawn in line ( 46 ) is first led by the pump ( 53 ) to the indirect heat exchanger ( 41 ) and then through line ( 54 ) to the indirect heat exchanger ( 26 ) before the heated water in line ( 17 ) Saturator ( 16 ) arrives.

From the sump of the saturator ( 16 ), circuit water is drawn off in line ( 56 ) with the aid of the pump ( 57 ) and a first partial flow is led through line ( 44 ) directly into the sprinkler cooler ( 43 ). The rest of the circulation water passes through line ( 58 ) to an indirect cooler ( 59 ), in which boiler feed water is heated, which is drawn off in line ( 60 ). This boiler feed water can be led through the line ( 34 ) into the collecting tank ( 33 ). Fresh water is added to the circuit water of line ( 61 ) through line ( 62 ) and the water is led through a further indirect cooler ( 63 ). Cooled water is drawn off in line ( 45 ) and a small partial stream is removed through line ( 64 ) before the remaining water is passed through line ( 45 ) to the cooler ( 43 ) in the manner already described.

The described method is very flexible for the simultaneous production of methanol and town gas from the same synthesis gas, whereby the production of one product can be varied at any time compared to the other product. The additional production of steam in saturated steam quality is also advantageous. If the conversion ( 22 ) and the methane synthesis ( 30 ) were to be connected in parallel, that is, starting from the synthesis gas of the line ( 15 ) each with a partial stream of this synthesis gas, one would obtain less favorable consumption figures.

example

In a procedure corresponding to the drawing without the plant ( 12 a), 300,000 kg of methanol and 600,000 Nm³ of city gas are produced per day. Details on generating the synthesis gas of line ( 10 ) remain open, the following data are partially calculated.

In line ( 10 ) 2763.6 kmol of synthesis gas are introduced per hour, the composition of which is given in Table 1 in column A and which has a temperature of 20 ° C. and a pressure of 25 bar:

Table 1

The synthesis gas of line ( 10 ) has a stoichiometric number S = 2.05. 1367 kmol / h of this gas are fed through line ( 11 ) to a conventional methanol synthesis plant, which is able to produce 300,000 kg of methanol per day. This results in 123.9 kmol / h of residual gas, which are discharged through line ( 14 ) and bring the amount of gas in line ( 15 ) to 1520.5 kmol / h. Column B in Table 1 gives details of this gas.

Temperatures and pressures in different lines are:

The results of the conversion ( 22 ) and methane synthesis ( 30 ) are calculated on the following basis:

The gas quantities in lines ( 25 ) and ( 27 ) behave as 7: 3. The data of the converted gas of line ( 24 ) are given in Table 1 in column C, column D gives the data of the gas in line ( 40 ) at. The drying ( 50 ) is carried out using glycol and the town gas that is available in line ( 51 ) includes the data in column E in table 1, the calorific value of the town gas is 4.07 kWh / Nm³.

The saturator ( 16 ) through line ( 17 ) gives 290.4 t / h of water at 197 ° C., so that the gas in line ( 19 ) contains 0.815 kg of steam per Nm³ of dry gas. The line ( 18 ) 2960 kg / h of water vapor of 250 ° C are fed. 262.7 t / h of water at a temperature of 149 ° C. are drawn off from the saturator ( 16 ) through the line ( 56 ), and the cooler ( 43 ) is led through the line ( 45 ) at 51.9 t / h of water of 50 ° C and through line ( 44 ) 206.8 t / h of 148 ° C. Since condensate is also formed in the cooler, 290.4 t / h of water, which has a temperature of 191 ° C., is drawn off through line ( 46 ).

16.5 t / h of saturated steam of 40 bar are generated in the heat exchanger ( 32 ) and are removed from the container ( 33 ) in the line ( 37 ). 13.5 t / h of water vapor are available in the line ( 37 a) for other use.

Claims (5)

1. A process for the production of town gas with a methane content of 20 to 50 vol .-%, whereby a solid, liquid or gaseous fuel is gasified by partial oxidation and a raw gasification gas is generated, which is dedusted, cooled and desulfurized and a desulfurized gas mixture is produced , which consists of at least 90 vol .-% of the gas components H₂, CO and CO₂, characterized in that one generates a synthesis gas whose concentrations of the gas components H₂, CO and CO₂ have a stoichiometric number S = (H₂-CO₂): (CO + CO₂) = 1.9 to 2.3 show that at least part of the synthesis gas is passed through a saturation zone, in which the synthesis gas is brought into contact with water of at least 100 ° C. and the synthesis gas is enriched with water vapor, so that the the saturation zone coming synthesis gas catalytically converted at 250 to 550 ° C that the converted synthesis gas in a first partial flow of 50 to 95% of the conver tated synthesis gas and a residual stream, that the first partial stream is passed through a catalytic methane synthesis which operates in the temperature range from 250 to 500 ° C., that at least part of the methane-containing gas coming from the methane synthesis is passed through a cooling zone together with the residual stream, in which the gas mixture is sprinkled with water which is withdrawn from the saturation zone and the methane-containing gas mixture withdrawn from the cooling zone is dried. 2. The method according to claim 1, characterized in that one of the partial streams from methane synthesis withdrawn methane-containing gas in the cycle back in leads the methane synthesis. 3. The method according to claim 1 or 2, characterized characterized in that one from methane synthesis coming methane containing gas producing Water vapor cools indirectly. 4. The method according to any one of claims 1 to 3, characterized characterized in that a part of the synthesis gas with S = 1.9 to 2.3 leads into a methanol synthesis and Produced methanol. 5. The method according to any one of claims 1 to 3, characterized characterized in that a part of the synthesis gas with S = 1.9 to 2.3 leads into a Fischer-Tropsch synthesis.