DE2530600A1 - Gasification of fossil fuels at elevated temp. and pressure - with high pressure steam contg. dissolved catalyst - Google Patents

Abstract

The steam press. is pref. 50-600 (70-300) bar. The catalyst may be a salt, pref. a borate, carbonate and/or hydroxide of an alkali metal, pref. K or of ammonium. Chalk may be added to the fuel to prevent reaction of the catalyst with the ash, or chemical adsorption. Gasification is pref. at 500-1100 degrees (600-900 degrees)C. Used esp. for prodn. of methane-rich gas to replace natural gas. Reaction rate is accelerated to at least that obtained without catalyst at lower pressure. The product gas is obtained at higher press. suitable for pipelines. Heat balance in the reactor is improved by the C + 2H2O CO2 + 2H2 reaction being favoured in preference to the more endothermic C + H2O CO + H2 reaction. Content of CO in the gas is reduced to below 2 vol. % making it more suitable for methanisation.

Description

Process for the catalytic pressure gasification of solid fuels with Steam.

During the early 1960s the situation emerged the energy market was characterized by large quantities of very cheap crude oil the 1973/74 energy crisis brought attention back to coal. The statistics the world energy reserves of fossil fuels shows that of the three types of fossil fuels Fuels Coal, crude oil and natural gas in coal about 5 to 10 times as much as stocks is present than in petroleum and natural gas. From the point of view of the various national Economic sectors is also the question of which access to the individual types of energy.

While large oil and gas deposits are only in a relatively small number of areas are concentrated in the world, coal reserves are more evenly distributed. the Differences in the reserves of the individual fossil fuels indicate that once With the shortage of crude oil and natural gas, more coal will be used got to. The liquefaction and gasification of coal as a conversion of a primary energy carrier in a secondary energy carrier of a different kind serves to relieve the demand after a shortage of oil and gas.

Recently, the development work on coal liquefaction and coal gasification due to the increased price level for liquid and gaseous Energy carrier received new stimulus. There is increasing interest primarily in Convert coal into methane-rich gas.

For the production of methane as a natural gas substitute from coal are for example The following two reaction paths are possible: 1) One path comprises the three process steps: a) Complete gasification of coal to CO + H2, b) Cessation of the methanation necessary CO / H2 ratio of 1: 3 through CO conversion, c) catalytic Methanation.

The gross reactions on which the individual process steps are based are listed below, including their enthalpy of reaction.

II) The second reaction path comprises the process steps: a) complete Gasification of coal or coke to CO + H2, b) conversion of the CO to H2, c) hydrogenation Gasification of fresh coal with the help of the generated hydrogen to CH4.

The gross reactions on which the individual process steps are based are listed below, including their enthalpy of reaction.

In both ways, the end product methane is generated from coal. Consequently the sum of the enthalpies of reaction is the same.

In reaction path II, the process takes place at a relatively high temperature The heat of reaction released by the gasification of the methane formation by hydrogenation for the overall process is used much better than that of path I, although larger, but relatively lower temperatures in the methanation step downstream of the gasification heat of reaction released. The usable efficiency is for the reaction path II is therefore greater overall under the conditions of practice. Besides, that's dem Gasification process from the outside to be supplied energy in path II only half as large as with path I. That means, based on the same production output, less exchange area for the heat transport or in the case of an autothermal process, a corresponding one lesser Oxygen consumption. This gives rise to the requirement when producing synthetic Natural gas as high a proportion of methane as possible through hydrogenation and not through To produce synthesis from CO + 3H2.

If the reaction is carried out appropriately - gasification under pressure in countercurrent of coal and gasification agents or gradual gasification - can be the thermodynamic advantageous methane formation through hydrogenation can be used in practice.

The following are used to convert coal into methane-rich gas Main process steps required: pretreatment of coal, gasification, conversion and methanation or hydrogenation.

During the pretreatment of the coal, the separation of rocks is carried out and understood the production of a suitable grain for the gasification process. The ability of the charcoal to bake is also important, which is sometimes difficult and unfavorable can be influenced. The grain size of the available fuel and its ability to be baked are co-determining whether the gasification of the coal in dormant bulk or can be done in the balance.

The gasification in countercurrent in stationary bed brings the advantages better heat utilization and more favorable kinetic conditions. The gassing of coal dust in suspension in a fluidized bed as a direct current process requires one higher heat demand and leads to a simultaneous decrease in the concentration of Carbon and gasifying agents under less favorable kinetic conditions.

For the most important processes, such as Lurgi pressure gasification, the Hygas process of the Institute of Gas Technology, the Koppers-Totzek method, etc., is the gasification reaction at pressures of about 50 bar and temperatures of 800 to 11000 C and performed above. The Lurgi process is an economically proven gasification process The Hygas process, still at the testing stage, promises to reduce the cost of the To lower gas generation. The Koppers-Totzek process and the Hygas process lead the Water vapor gasification in the fluidized bed, while after the Lurgi process in the dormant Bed is gasified in countercurrent.

Mixtures of oxygen and water vapor are used as gasification agents used; Mixtures of water vapor can also be used to generate lean gas and air can be used. The added oxygen partially generates through this Combustion of the coal the reaction temperature and the heat of reaction necessary for the endothermic reaction between coal and water vapor is required. In principle is it is also possible to supply the required process heat from the outside. Here offers the use of nuclear heat is a much-noticed new aspect.

In the Lurgi process, coal is passed through in a bed moving downwards gasifies an upwardly flowing stream of oxygen and steam. The ashes will removed by a rotating grate at the bottom of the gasification zone. That head The raw gas leaving the gasifier is washed with oil to remove tar, heavy oil and remove entrained solids. The gas composition is changed by changing of the ratio 02 / steam corrected. After the removal of C02 and H2S the gas methanates to produce substitute natural gas.

In the Hygas process, coal is produced in two fluidized bed reactors connected in series gassed. The residual coke from coal gasification is used to make hydrogen by steam gasification for the steps of further gasification. The raw gas from the reactor is quenched to remove oil and then purified from acid gases.

Thereafter, CO is partially converted and after separation of the resulting C02 methanated. At the increased pressure of 75 bar in the reactor and 6500 C or 950 up to 10000 C Reactor temperatures also play a role in the hydrogenation of the coal a noticeable role in the process flow.

In the Eoppers-Totzek process, coal dust is mixed with oxygen Addition of steam in a 'reaction flame' gasified in front of a nozzle. As a carrier gas the gasification oxygen is used for the coal dust. With this procedure you can all coals can be processed regardless of their baking ability.

The gasification takes place at normal pressure. In the reaction flame the temperature is very high; as a result, the C4 content remains in the raw gas below 0. t% OH4. All the methane needed to use the product as a substitute natural gas must be generated by methanation.

Depending on the process, the raw gases contain different proportions Carbon monoxide, hydrogen, methane, carbon dioxide and unreacted water vapor and, depending on the gasification agent, sometimes also higher proportions of nitrogen. Of the The sulfur contained in the feed fuel is found to a greater extent in the gas than Hydrogen sulfide and in small amounts as carbon oxide sulfide and must be from the Raw gas can be removed by gas scrubbing.

Together with the gaseous sulfur compounds, the existing Washed out carbon dioxide.

In general, the following reactions are important for gasification: Table 1 Standard enthalpy of reaction Reaction Heat of reaction Reaction temperature #H Influence of kcal / pressure mol 1) C + O2 # CO2 strongly exothermic high -97.0 0 2) C + CO2 # 2CO strongly endothermic high - PCO negative 3) C + H2O # CO + H2 strongly endothermic high +28.41 P (CO + H2) negative 4) CO + H2O # CO2 + H2 slightly exothermic high / medium -9.80 0 5) Hydrogenation to CH4 exothermic high / medium -49.27 6) CO + 3H2 # CH4 + H2O strongly exothermic medium / low PH2 positive 7) C + 2H2O # CO2 + 2H2 endothermic high +18.53 PCO2 negative 8) C + 2H2 # CH4 exothermic high / medium -20.6 PH2 positive 9) 2C + 2H2O # CH4 + CO2 - high -2.1 0 The mentioned reaction enthalpies relate to coking carbon and deviate by about 3 kcal / mol from the standard enthalpies related to graphite.

The main reaction of gasification, namely implementation is strongly endothermic according to Table 1 and only takes place at a technically usable rate above 750 to 8000 C. The amount of heat required for the reaction can be supplied by the following measures: a) combustion of part of the solid fuel by means of oxygen or air (autothermal gasification) b) heating of the reactor from the outside with heat flow through the wall of the reactor or by means of special heating elements, c) circulating solid, liquid or gaseous heat transfer media.

All of these possibilities have already been investigated and put into practice tried. Autothermal gasification with oxygen has become widely accepted and steam. The supply of high-temperature core heat is under development by means of external heating. However, special attention is also paid to increasing the carburetor throughput given. While the Lurgi pressure carburetor in operation is printing from Working at 30 bar and temperatures of 700 to 10000 C is the goal of the new American Works that require gasification below that required for feeding into a long-distance gas network Pressure, i.e. below 70 bar and more.

Carrying out the gasification process at higher water vapor pressures however, generally leads to a reduction in the rate of the reaction. The diminution the rate of reaction at higher water vapor pressures has so far allowed work appear uninteresting at higher pressures. However, if one sets according to the procedure this invention to the high-tension water vapor compounds that are in it dissolve and accelerate the reaction between coal and water vapor, so can high water vapor pressures reaction rates to be achieved which are even faster than the reaction rates at lower pressures and same temperature.

The amount of catalyst in the steam preferably corresponds to the saturation concentration or comes close to it.

Among the substances that are produced by the method of this invention in both high-tension water vapor are readily soluble as well as based on the reaction between Coal and water vapor have good catalytic properties, the salts belong to the Alkalis. Primarily suitable are the hydroxides, borates, including potassium tetraborate, and carbonates, including bitarbonates, of the alkalis. Certain reaction acceleration also show the alkali chlorides. Of these, in turn, have carbonates and hydroxides particularly interesting properties of potassium. For example, in water vapor from 8250 C and 150 bar 0.007 g of potassium hydroxide dissolved in 1000 g of water.

Although the amount of salt dissolved in the water vapor under these conditions is very low, compared to gasification at 30 bar water vapor pressure, a Get sales acceleration by a factor of four. The result of the addition of the catalysts The effect of an increase in the reaction speed corresponds to an increase in the speed, which is achieved by increasing the temperature by approx. 150 to 2000 C. The one in the Alkali compounds contained in coal ash, mainly silicates, tend to show an inhibition of the reaction.

Surprisingly, it is also found that - after the process of this Invention the composition of the raw gas changes in such a way that more hydrogen and carbon dioxide and less carbon monoxide is produced. The content of the raw gas Carbon monoxide decreases to values of less than 2% by volume.

This would make the raw gas particularly suitable for the production of synthetic Natural gas should be suitable according to the thermodynamically more favorable route II. Apart from this it is possible by the process of this invention without sacrificing gasification capacity Apply gasification pressures in the amount required for further use of the finished product are desirable.

In addition, the heat balance of the carburetor is due to the preference of Response 7 improved over response 3.

In one that works with counterflow of coal and gasifying agent Carburetor becomes a high one in the lower part, to which the gasifying agent is supplied Water vapor pressure prevail and the catalyst according to this invention in the gas phase be resolved. As conversion takes place, the rising gas stream becomes water vapor impoverish and decrease the solubility of the salts in the gas stream. The carried catalyst falls out and settles in finest distribution on the coal. The coal then transports it back to zones with high water vapor partial pressure, where it goes back into solution. In this way the catalyst of this invention becomes circulated in the carburetor. Only the losses caused by adsorption to the Ash and being lost as dust through entrainment in the raw gas must be replaced. The losses on the catalyst through adsorption on the ash components or through Reaction with the ash components can be beneficial by adding lime to the Coal can be decreased.

The one on the fresh coal by precipitating in the finest distribution deposited catalyst accelerates the reaction between coal and water vapor also effective.

In principle, the method of this invention is also applicable to steam gasification of heavy oils, oil residues, oil shale etc. applicable. The procedure is based on The following examples are explained without restricting the scope of application to be prejudiced: Example 1 At a pressure of 600 bar and a temperature of 6600 C becomes water vapor, which is saturated in potassium hydroxide, with ground brown coal briquettes reacted in an autoclave. This is produced per liter of lignite fill after separating the water vapor, 4 liters of NTP gas per minute, which is 23% by volume Contains methane, 0.7% by volume ethane, 34% by volume hydrogen and 42% by volume carbon dioxide. In addition, small amounts of higher hydrocarbons are produced. Comparatively will at the same temperature and 70 bar per minute 2.5 liters of NTP of a gas that Contains 46% by volume hydrogen, 6% by volume carbon oxide, 11% by volume methane and 37% by volume C02, obtained per liter of brown coal fill.

Example 2 At a pressure of 400 bar and a temperature of 6300 C becomes water vapor that is saturated with potassium hydroxide (approx.

0.16 g / 1000 g H20), with ground brown coal in an autoclave brought to reaction. Per liter of lignite fill produced every minute 2.5 liters of NTP of a gas which, after deduction of the water vapor, 20 vol .-% methane, 38 Contains vol .-% hydrogen, 41 vol .-% carbon dioxide and 1 vol .-% ethane. Also arise still small amounts of higher hydrocarbons. Comparatively are at the same Temperature and 70 bar per minute 2 liters of NTP of a gas containing 4% by volume of methane, Contains 61% by volume of hydrogen, 34% by volume of carbon dioxide and 1% by volume of carbon oxide, per Liters of lignite bulk received.

Example 3 At a pressure of 300 bar and a temperature of 7500 C becomes water vapor in which sodium hydroxide is dissolved at the saturation concentration is reacted with ground hard coal coke in an autoclave. Per Liters of eoksschüttung are produced per minute 1.9 liters of NTP of a gas that after condensation of the water vapor 1 vol .-% methane, 65 vol .-% hydrogen and 33 Contains% by volume of carbon dioxide.

(In addition, small amounts of higher hydrocarbons are formed). For comparison, at the same temperature and 70 bar without sodium hydroxide in the minute 0.4 liter NTP of a gas containing 3% by volume methane, 59% by volume hydrogen, Contains 11% by volume of carbon oxide and 27% by volume of carbon dioxide per liter of coke bed obtain.

Example 4 At a pressure of 300 bar and a temperature of 7700 C becomes water vapor, in which potassium hydroxide with the saturation concentration is dissolved is reacted with ground hard coal coke in an autoclave. Per Liters of coke fill this produces 6.1 liters of NTP of a gas per minute that after condensation of the water vapor 5 vol.-76 methane, 60 vol.hydrogen and 35 Contains% by volume of carbon dioxide. In addition, small amounts of higher hydrocarbons are produced. In comparison, at the same temperature and 300 bar without potassium hydroxide in the minute 0.5 liter NTP of a gas containing 4% by volume methane, 58% by volume hydrogen, Contains 26% by volume of carbon dioxide and 12% by volume of carbon oxide, per liter of bed obtained ground coal coke.

Example 5 At a pressure of 70 bar and a temperature of 7500 C becomes water vapor, in which potassium hydroxide with the saturation concentration is dissolved is reacted with ground hard coal coke in an autoclave. Per Liters of eoksschüttung produce 1.6 liters of NDP per minute of a gas that after condensation of the water vapor 1% by volume methane, 64% by volume hydrogen, 2% by volume Contains carbon monoxide and 32% by volume carbon dioxide. In addition, there are still minor ones Amounts of higher hydrocarbons. Comparatively, be without the presence of potassium hydroxide at the same temperature and 70 bar per minute 0.4 liters of NTP of a gas that 3 vol .-% methane, 59 vol .-% hydrogen, 11 vol .-% carbon oxide and 27 vol .-% carbon dioxide contains, obtained per liter of ground hard coal coke.

Example 6 At a pressure of 150 bar and a temperature of 8250 C becomes water vapor, in which potassium hydroxide is dissolved up to the saturation concentration is reacted with ground hard coal coke in an autoclave. Per Liter of eoksschüttung produce 5.1 liters of NTP per minute Gas, after condensation of the water vapor 1.5 vol .-% methane, 64 vol .-% hydrogen, Contains 2% by volume of carbon monoxide and 32.5% by volume of carbon dioxide. Also arise still small amounts of higher hydrocarbons. Comparatively being without attendance of potassium hydroxide at the same temperature and 150 bar per minute 1.2 liters of NTP a gas containing 2% by volume methane, 61% by volume hydrogen, 11% by volume carbon monoxide and contains 26 vol .-% carbon dioxide, per liter bed of ground hard coal coke obtain.

Example 7 At a pressure of 300 bar and a temperature of 8250 o Water vapor is dissolved in the potassium hydroxide with the saturation concentration is reacted with ground hard coal coke in an autoclave. Per Liter of coke fill 10.3 liters of NTP of a gas per minute that after condensation of the water vapor 1.8 vol .-% methane, 64 vol .-% hydrogen, Contains 1.55% by volume of carbon monoxide and 32.7% by volume of carbon dioxide. Also arise still small amounts of higher hydrocarbons. Comparatively being without attendance of potassium hydroxide at the same temperature and 300 bar per minute 1.6 liters of NTP a gas containing 2.5% by volume methane, 62% by volume hydrogen, 6% by volume carbon monoxide and contains 29.5% by volume of carbon dioxide, per liter of bed of ground hard coal coke obtain.

Example 8 At a pressure of 600 bar and a temperature of 6200 C is an aqueous ammonia solution, which consists of 11 wt .-% of NH3, with ground Lignite reacted in an autoclave. Per liter of lignite bulk This creates 0.85 liters of NTP of a gas per minute that contains 38% by volume of hydrogen, Contains 42 vol .-% carbon dioxide, 14 vol .-% methane and 6 vol .-% ethane. Also arise still small amounts of higher hydrocarbons. In comparison, the same temperature and pressure without ammonia per minute 0.5 liters NTP of a gas that contains 32% by volume Hydrogen, 43% by volume carbon dioxide and contains 25 vol .-% methane, obtained per liter of bulk brown coal.

- patent claims -

Claims (8)

P a t e n t a n s p r U c h e li Process for gasifying fossil fuels Fuels with water vapor at elevated pressures and temperatures, characterized in that high-pressure steam is used in which suitable catalysts are dissolved are. 2. The method according to claim 1, characterized in that the water vapor pressure 50 to 600 bar, preferably 70 to 300 bar. 3. The method according to claim 1 and 2, characterized in that as Catalysts that are soluble in high pressure water vapor, salts of alkali metals, preferably borates, carbonates and / or hydroxides can be used. 4. The method according to claim 1 and 2, characterized in that as Catalysts which are soluble in still water vapor, the borates, carbonates and hydroxides of potassium can be used. 5. The method according to claim 1 and 2, characterized in that as Catalyst ammonia, borates and / or carbonates of ammonia can be used. 6. The method according to claim 1 to 5, characterized in that the Catalysts soluble in high pressure steam can be used in a mixture. 7. The method according to claim 1 to 6, characterized in that the Lime is added to the gasification fuel to cause a reaction of the Catalysts with the ash components or chemical adsorption of the same to prevent the ash components. 8. The method according to claim 1 to 7, characterized in that the Gasification at temperatures of 500 to 11000 C, preferably at temperatures of 600 to 9000 C. / -