Compression of synthesis gas

Because of the SNG specification a relatively high pressure is preferred, but compression of synthesis gas was uneconomical compared with final SNG compression. The pressure during methanation is governed by the pressure of gasification and the pressure drop across upstream plants. 

Hydrocarbon Research Inc., elected partial oxidation for the Carthage Hydrocol plant at Brownsville. After initial experiments that Hydrocarbon Research conducted at Olean, New York, The Texas Company assumed responsibility for further development of partial oxidation at its Montebello, California, laboratory, under duBois ( Dubie ) Eastman. For conversion of natural gas to gasoline by Fischer-Tropsch synthesis, partial oxidation s advantage over steam-methane reforming lay in its ability to operate at a pressure approximating that of the synthesis, thereby essentially eliminating need for compression of synthesis gas. 

Compression of synthesis gas. The synthesis gas composed by hydrogen and nitrogen is compressed to required pressures, usually 10-30 MPa, by piston-type or centrifugal compressors. During ammonia synthesis, single-pass conversion is only 10%-20%, and therefore, most of the synthesis gas must be recycled, compressed and returned to the synthesis loop again. 

S. Singh (Battelle Memorial Institute) What is the panel s opinion of compressing the synthesis gas before methanation rather than after For example, feed the methanator at 1000 psig, the final line pressure of the pipeline gas, rather than at some lower pressure such as 400 psig at which the synthesis gases are purified ... 

Sulphur is detrimental to the sjmthesis and trace amounts of sulphur are removed using zine oxide prior to synthesis. After the production of synthesis gas, the methanol sjmthesis requires compression to about lOObar. The methanol synthesis loop con rises a reactor, a separator and recompression of the reeyele gas. A purge gas can be used to produce power supplemented by steam raised in the methanol reactor and the coal gasifier. The crude methanol produced can be upgraded to chemical grade product by distillation. The intermediate methanol is passed into storage. The reaction stoichiometry is ... 

Methanolation [744], [745] has been proposed for partially replacing methanation. It converts the residual carbon oxides to methanol, preferably at higher pressure in an intermediate stage of synthesis gas compression. Methanol is removed from the gas by water scrubbing. The methanol may be recycled to the steam reformer feed or recovered as product. As full conversion of the carbon oxides is not achieved, a clean up methanation unit must follow the methanolation section. 

The gas engine will be operated with mixtures of synthesis gas and natural gas and detailed measurements of cylinder pressure, compression ratio and heat released by the engine are planned in addition to emission measurements of CO, unburned hydrocarbons and NO,. The dependency of the results on the ratio of synthesis gas/natural gas will further be evaluated. 

The exothermic reaction between nitrogen and hydrogen occurs in the presence of suitable catalysts and results in volume reduction, the highest ammonia concentrations being obtained at the highest possible pressure and the lowest possible temperature. The upper limit for the applied pressure is determined by the cost of compression of the gas mixture and the cost of the high pressure plant. The reaction temperature is determined by the type and activity of the catalyst. The removal of ammonia from the reaction gas should be as complete as possible to favor the fresh formation of ammonia. Other important parameters are the contents of inert gas and oxygen compounds in the unreacted synthesis gas. 

The industrial scale reaction of synthesis gas to ammonia in pressure reactors takes place in a cyclic process in which the ammonia formed is removed from the reaction gas and the unreacted synthesis gas returned to the reactor. In addition to the ammonia formed, inert gases and the liberated reaction heat have to be continuously removed from the cyclic process. The excess heat of the product gas is used to heat the feed synthesis gas to the reaction temperature in a heat exchanger integrated into the reactor. Additional waste heat can be utilized for steam generation. The pressure loss in the synthesis gas due to its passage through the synthesis loop is compensated for and the fraction of synthesis gas converted replaced by fresh compressed synthesis gas ( fresh gas ). 

The methanol synthesis reaction requires compression of the gas mixture to 200-330 atm, temperatures in the region of 300°C, and a catalyst, such as... 

Because the compressibilities of the gas, liquid, and solid phases differ, the structure of the equipment used with each of these phases is very different. In addition, specific modifications have been developed according to (i) the objective of the high-pressure studies (synthesis, crystal growth, or physical measurements), and (ii) the chemical nature of the medium. 

Feed for this heavy-water plant consists of synthesis gas for the ammonia plant of the Indian Department of Atomic Energy, at 190 to 200 atm. The heavy-water plant, however, operates at 300 atm. To avoid the need for compressing synthesis gas, and to isolate gas flow in the ammonia plant from gas flow in the heavy-water plant, deuterium in feed synthesis gas is transferred to a solution of potassium amide in ammonia in the transfer column A, and synthesis gas 85 percent stripped of deuterium is returned to the ammonia plant. 

In the above section, the importance of carbon monoxide and carbon dioxide conversion and the technically attainable approach to the equilibrium has been described. However, these two parameters alone do not decide upon the optima-tion for the production of methanol from a specific synthesis gas. The methanol yield from the synthesis gas is of quite decisive importance for economically producing methanol on a commercial scale. Its this yield on which depend the quantity of synthesis gas which must be produced horn coal, cleaned, conditioned and compressed and the quantity of CO2, CO and H2 which must be removed from the methanol synthesis as purge gas and thus is lost to methanol production by the direct route. 

The loop pressure has an important influence on the performance of the ammonia synthesis loop because of its influence on the reaction equilibrium, reaction kinetics, and gas/liquid equilibrium in the product separation. Actual selection of loop pressure is in many cases a compromise between selecting a high pressure to favour the ammonia synthesis reaction, and on the other hand selecting a reasonable pressure to minimise the compression power of the synthesis gas compressor, which compresses the synthesis gas to the desired loop pressure. The loop pressure also has a significant impact on the ammonia refrigeration system, since a high loop pressure favours condensation of the ammonia product in the loop water cooler and saves compression power on the refrigeration compressor. On the other hand, a low loop pressure saves compression power on the synthesis gas compressor, but increases the... 

Drying of Synthesis Gas - No water is allowed to enter the synthesis converter because of its adverse effect on the catalyst. The older plants used to remove the residual water by mixing the makeup synthesis gas with the converted gas ahead of the ammonia condensation and separation. However, it required more compression power since converter effluent undergoes recycle compression before product condensation. It also diluted the ammonia concentration of the converted gas and resulted in a lesser amount of ammonia condensed and higher recycle flow rates. Most modern plants use molecular sieve dryers to remove water in the synthesis gas to less than 1 ppmv. The sieves are usually located at the interstage of the synthesis gas compressor [4[. The dried makeup gas can then be combined with the recycle and sent directly to the ammonia converter. 

The compressed gas is methanated and then cooled and dried by a molecular sieve. The catalysts used in the production of synthesis gas are all conventional. 

This excess hydrogen is normally carried forward to be compressed into the synthesis loop, from which it is ultimately purged as fuel. Addition of by-product CO2 where available may be advantageous in that it serves to adjust the reformed gas to a more stoichiometric composition gas for methanol production, which results in a decrease in natural gas consumption (8). Carbon-rich off-gases from other sources, such as acetylene units, can also be used to provide supplemental synthesis gas. Alternatively, the hydrogen-rich purge gas can be an attractive feedstock for ammonia production (9). 

Ammonia Synthesis and Recovery. The purified synthesis gas consists of hydrogen and nitrogen in about 3 1 molar ratio, having residual inerts (CH Ar, sometimes He). The fresh make-up gas is mixed with the loop recycle and compressed to synthesis pressures. AH modern synthesis loops recycle the unreacted gases because of equiUbrium limitations to attain high overall conversions. The loop configurations differ in terms of the pressure used and the point at which ammonia is recovered. 

The purified synthesis gas is cooled and the condensed water is removed. The syngas is then compressed in a series of centrifugal... 

The purified syn gas next flows to the final production stage, which is anunonia synthesis and recovery. The first step is compression of tlie syn gas. Synthesis pressures range from 2000 to 10,000 psi depending on the quality of tlie syn gas and certain otlicr conditions, such as production requirements per converter," ... 

Gas recirculation in the anunonia synthesis section is necessary because only 9-30% conversion is obtained per pass over tlie catalyst." There are two tj pes of synthesis loops. One type recovers anunonia product before recycle compression. Inerts entering witli tlie makeup gas are removed with a purge stream. The ammonia is recovered by condensation, which requires refrigeration. Since airliydrous anunonia is readily available, it is normally used as tlie refrigerant. 

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