SE449740B - PROCEDURE FOR PREPARING A SYNTHESIC GAS FLOW FOR MANUFACTURING AMMONIA - Google Patents

Description

449 740 2 -n The attack reforming process can alternatively be carried out fully or partially autothermally, by the introduction of air and / or oxygen to allow combustion inside the catalytic reactor.

Specifically in the production of ammonia synthesis gas from natural gas the indirect heat supply to the reactants in the primary reformer by internal combustion of air in it the secondary reformer, which adds i.a. the need for nitrogen to the ammonia synthesis process. In another steam reforming process takes place all high-temperature heating required by autothermal heating combustion of oxygen or oxygen-enriched air in the catalyst zone and no indirectly heated reformer was used.

The reformer product gas is subjected to CO conversion, CO - 2 removal and final purification, e.g. methanation depending on the needs of different uses.

B. Partial oxidation The partial oxidation processes are based on combustion the supply of hydrocarbon with a limited supply of oxygen or air. Examples of such processes are Texacos and Shells processes, which can receive all types of hydrocarbons from natural gas to coal and others, such as Koppers-Totzek's and Lurgis' see, which are specific to carbon.

Because no catalyst was used in these processes the sulfur content of the feed hydrocarbon is not critical.

The product gases from the partial oxidation processes contains hydrogen, carbon oxides, residual methane and steam in various portions, and with sulfur compounds, mainly hydrogen sulphide, to the extent that sulfur is present in the feed as well as others trace contaminants. Especially in the case of Lurgis and other processes, where carbon is kept in the carburettor at relatively low temperatures products, the product gases may contain significant amounts of high molecular weight learned organic material, such as benzene and tar. the desire to free the product gas from trace contaminants together with the difficulty of using a low-temperature carbon monoxide exchange catalyst associated with sulfur-containing gases, i.e. at temperatures about 200 - 250OC, has often led to that a nitrogen scrubber was used for the final gas purification after the exchange reaction and the removal of carbon dioxide and hydrogen sulphide, compare the use of methanation in connection with steam reforming. 449 740 It should be noted that when using the partial the oxidation processes and the autothermal vapor reforming processes as described above, the use of air as an internal oxidant limited by the extent to which the present result nitrogen can be accepted in the product gas.

Thus, in the ordinary, natural gas-based ammunition process, the amount of air fed into the secondary transformer to the nitrogen supply required for ammonia the synthesis step. Also in the partial oxidation and autothermal reform operations, it is usually necessary to seize at least a partial supply of the oxidant in the form of essentially pure oxygen, except when the process is only to be used to produce a low-grade fuel gas. The necessity to supply substantially pure oxygen means that an air separation facility must be installed. Additional capital and operating costs that this entails, results in such processes become less attractive as a means of producing hydrogen rich gases, except when hydrocarbon feed is very cheap or complete flexibility is desired with respect to the raw material the source.

An exception to this limitation is the Brauns' Purifier Process "for the production of ammonia described in U.S. Pat. 3,442,613. In this process, a synthesis gas stream is obtained by pri- more reforming of methane or another hydrocarbon with steam followed of a secondary reform, where air is present in a quantity which gives a stoichiometric excess of nitrogen of 2 - 150 mol percent, based on the amount required for the synthesis gas. the excess nitrogen is condensed downstream of the deformer.

An object of the present invention is to achieve a method of producing a gas stream suitable for ammonia synthesis.

According to an embodiment of the present invention a process is produced for the production of a gas stream for ammonia synthesis, which process is mainly characterized by The hydrocarbon reaction with air involves the partial oxidation of a substance, selected from a group consisting of oil, coal, natural gas or any combination thereof, in the presence of air at a pressure of 15 to 150 bar and at a temperature of 300 ° C to 2000 ° C to form a crude gas stream, containing hydrogen and nitrogen 449 740 -1- with a stoichiometric excess of nitrogen of at least 200 mole percent, based on the amount required for ammonia synthesis, wherein it dried crude gas stream is introduced into a cryogenic separator at a pressure of 15-1000 bar, in which it is divided to give two currents as leaves the cryogenic separator, namely (1) the synthesis gas stream at a pressure of 15-100 bar and (2) a nitrogen-rich waste stream at one pressure of 5-50 bar, which nitrogen-rich stream is heated to a temperature 500 ° C-2000 ° C and expanded in a turbine to generate power.

According to another embodiment of the invention a method of producing a gas stream suitable for ammonia synthesis, comprising generating a gas stream consisting essentially of nitrogen and hydrogen, where the nitrogen is present in an excess of 200 mol percent calculated on the quantity required for ammonia synthesis at a pressure of at least 15 bar, preferably 30-100 bar, feed converting the gas stream to a separation step where some of the nitrogen condensed to give a hydrogen-nitrogen gas stream at a pressure which substantially corresponds to the pressure before the separation step, in The hydrogen nitrogen ratio is suitable for ammonia synthesis and a nitrogen flow at a pressure of up to 50 bar, preferably 5-10 bar, feeding the hydrogen-nitrogen gas stream into an ammonia synthesis reactor and heating the nitrogen stream to a temperature of up to 200 ° C, preferably 50 ° C, and possibly expansion in a bees for power generation.

The invention is based on the fact that hydrogen and nitrogen mixtures can easily be separated, due to the large differences in their properties and that the nitrogen content of such mixtures thereby can be checked carefully. The easiest way to separate the gases is by cryotechnical treatment, although other separation methods, which is based on the difference in the molecular size of the gases, e.g. methods which use different adsorption or diffusivity, can also be used das. The invention allows the use of any gas which, in addition to the major part contains hydrogen and nitrogen, and the gas source can therefore derived from partial oxidation of oil, coal or gas in air.

In a preferred embodiment, the desired one is separated the amount of nitrogen in a cryogenic separator. The separator can use Joule Thom / son cooling and regenerative heat exchange, low temperature processing expanders, additional cooling or combinations thereof. Such cryogenic separators 5,449,740 -a are well known and commercially available. It avsepareradë ' the hydrogen, which contains the desired quantity of nitrogen, leaves normally the cryogenic separator at a slightly lower pressure than inlet pressure and fed into an ammonia synthesis system.

The nitrogen stream which normally leaves the cryogenic at a slightly lower pressure than the inlet pressure, but as can still provide useful power, when heated and ma- taken through an expansion turbine.

The process according to the invention has a number of advantages against the process described in U.S. Pat. No. 5,442,615. The test gas according to the invention can be obtained by partial oxidation. dation, i.e. combustion, of a large number of hydrocarbons carbon, which is less complex than the catalytic the path of reforming and the sulfur content of the feed carbon the hydrogen is not critical because no catalyst was used.

Combustion can be carried out in a single step, whereby pri- mare and secondary reformers do not need to be used. During that the amount of air used in the combustion stage gives in an amount of at least 200 mole percent in excess in to synthesis gas needs, this large amount can be Gunpowder is used to generate useful power after the separation step, since it is at a higher pressure compared to the previously known process, whereby it contributes to the economy of the overall system.

The invention will now be described in more detail below in connection to the accompanying drawings, in which Fig. 1 shows a flow chart of a process in accordance with the invention, Fig. 2 shows a flow chart of an alternative process in one similarity to the invention and Fig. 5 shows a schematic view of a gas turbine operating at high temperature in an open cycle, which is suitable for use in the process according to the finding.

Referring to Fig. 1, natural gas, oil is oxidized or carbon or a combination thereof partially with air or oxygen-enriched air, which is usually preheated and compressed.

The resulting gas stream contains hydrogen, nitrogen, carbon monoxide, methane and hydrogen sulphide, if svayel is present, wherein nitrogen is present in an excess of at least 200 mole percent over what is required for ammonia synthesis. The partial the oxidation process is carried out at a pressure of up to 150 449 740 e bar, normally 15 - 150 bar, preferably 5o - 1oo bar, -ocn ff at a temperature of 500 - 2 O00 ° C, normally up to 1 00000.

The oxidation can be carried out at atmospheric pressure, in which case the gas stream can be compressed at a later stage in the treatment. processes. “ The resulting gas stream is passed over an exchange tea catalyst, e.g. iron oxide or cobalt molybdate, normally at a temperature in the range 200 - 50,000 for conversion of present carbon monoxide to carbon dioxide and hydrogen. The gas flow is then traded for the removal of carbon dioxide and hydrogen sulphide pollutants. There are many different types of processes for such gas removal, including scrubbing with hot potassium carbonate, for example at 70 - 11000, and the Rectisol process. Sulfur content the gas can be removed at any previous step. Possibly- residual carbon oxides can be removed by methanation, at 250 - 45000. The resulting gas comprises a mixture of hydrogen and nitrogen, with methane, inert gases such as gon and water vapor as the main pollutants. This gas is dried then by cooling initial and subsequent contact with a drying medium, e.g. a molecular silad sorbent, which is also le remove any remaining traces of carbon dioxide. The tor- the gas is then fed to a cryogenic nitrogen / hydrogen separator, which e.g. uses cooling according to Joule Thomson and regen- rative heat exchange. The gas is brought into contact with the heat exchanger element, which cools the gas to about 100 K. In the cryogenic con- the nitrogen content of the hydrogen is reduced to the level required for the ammonia synthesis gas, typically 25% N2 for the ammonia showed. The cryogenic nitrogen condensation results in partial depletion of the methane and argon content in the inlet gas, at the removed contaminants appear in waste nitrogen the current. The hydrogen-nitrogen stream, which leaves the condenser at one slightly lower pressure than the inlet pressure of the gas stream, is injected into an ammonia synthesis system.

In the embodiment shown in Fig. 2, the nitrogen comprises the condenser a type of liquid nitrogen wash to remove Ä residual carbon monoxide to a level acceptable for ammonia showed. This solution allows methanation to be ruled out and allows the beneficial use of a higher CO level for the exchange conversion and results in a final synthesis GAS SOTD V-â-.Sently free of CHQ and ingrtgaser, The pure 449 740 7 the nitrogen required for the washing can be conveniently obtained from the condensed nitrogen in the cryogenic separator, var- by no dependence arises from an external source of liquid nitrogen, as in the classic nitrogen washing plants.

It is also possible to place the cryogenic nitrogen the condensation upstream of the methane ring in Fig. 1.

In all applications, it is advantageous if the waste the nitrogen is discharged from the cryogenic condenser near the environment. temperature and at an elevated pressure of up to 50 bar, usually 5 - 10 bar, as it can then be heated to a suitable inlet temperature for a high temperature turbine and expanded therein to near atmospheric pressure, so as to generate a large part of the force required for compression ring of the gas stream, e.g. to compress the process air for the partial oxidation or steam reforming steps.

The waste nitrogen can be heated to the turbine inlet temperature. raturen, e.g. 500 - 2 000C, normally 500 - 1 000C, by indirect heat exchange and / or by direct combustion of its combustible content, i.e. traces of methane, hydrogen, carbon monoxide with added air and additional fuel, if required, upstream of the turbine.

In the arrangement of the expansion turbine, shown in Fig. 5, the hot gas expansion turbine is the turbine element of a open-cycle gas turbine. Nitrogen is mixed with additive fuel and fed to the combustion chamber of the gas turbine as fuel.

At the same time, the process air requirement for the partial oxidation the gas turbine compression or reforming processes sorutmatningen. Through this arrangement, approximate relative parity between the mass flows in the compressor and expansion sections of the gas turbine and an efficient device for compression and expansion are achieved by means of well-developed load industrial equipment.

Alternatively, waste nitrogen can be expanded at a low temperature. peratur, e.g. ambient temperature, to generate power and used to cool desired parts of ammonia synthesis tesanläggpíngen.

If the waste carbon dioxide from the acid-gas removal plant the disposition would be emitted to the atmosphere in impure form, it is appropriate to use the waste nitrogen under pressure from the the separator to remove a significant portion of the carbon 449 740 8 - v the oxide from the washing solution and then feed the combined "- nitrogen and carbon dioxide flow, still at high pressure, for heating and work expansion.

In summary, the following benefits are offered for oxidation / nitrogen condensation / nitrogen expansion system as written compared to normal practice, including oxidation of a raw material: Elimination of air separation system, oxygen compressors, pipelines, etc. 2. Reduction of the total installed force in plant compressors can be achieved in many cases. 5. In view of the high potential efficiency for the expansion of the waste nitrogen containing the gas and conventional, associated heat recovery, a significant reduction of the entire plant's total energy needs obtained. v

Claims (9)

449,740 Claims A process for producing a synthesis gas stream for the production of ammonia, comprising reacting hydrocarbons with air in an amount sufficient to substantially reduce the amount of hydrocarbons and to provide a stoichiometric excess of nitrogen beyond that required for ammonia synthesis, treatment of the resulting crude gas stream to remove carbon oxides, drying the crude gas stream and cooling the gas stream so that residual hydrocarbons and nitrogen are condensed therefrom to obtain the synthesis gas stream for ammonia production, characterized in that the reaction of the hydrocarbons with air involves partial oxidation of a substance selected from a group consisting of oil, coal, natural gas or any combination thereof, in the presence of air at a pressure of 15 to 150 bar teh at a temperature of ~ 30 ° C to 2000 ° C to form an intake stream, containing hydrogen and nitrogen with a stoichiometric excess of nitrogen of at least 200 mole percent, based on the an amount required for ammonia synthesis, the dried crude gas stream being introduced into a cryogenic separator at a pressure of 15 to 1000 bar, in which it is divided to give two streams leaving the cryogenic separator, namely (1) the synthesis gas stream at a pressure of 15 to 100 bar and (2) a nitrogen-rich waste stream at a pressure of 5 to 50 bar, which nitrogen-rich stream is heated to a temperature of 50 ° C to 2000 ° C and expanded in a turbine to generate power. 2. A process according to claim 1, characterized in that the crude gas stream resulting from the partial oxidation is fed over a replacement catalyst and reacted with steam at elevated temperature to convert the carbon monoxide present in the crude gas stream to carbon dioxide and hydrogen. 3. A process according to claim 2, characterized in that the crude gas stream after passage over the exchange catalyst is subjected to scrubbing with hot potassium carbonate at a temperature of 70 - 11000 to remove the acid gas content before the separation step. 4. A method according to claim 3, characterized in that the raw gas stream after scrubbing with hot potassium carbonate is subjected to washing with liquid nitrogen to remove carbon monoxide in the raw gas stream before the separation step. 5. A method according to claim 4, characterized in that the separation step is carried out in a cryogenic separator and that the liquid nitrogen in the washing step is obtained from the nitrogen condensed in the cryogenic separator. Process according to Claim 3, characterized in that the crude gas stream, after scrubbing with hot potassium carbonate, is subjected to methanation in order to remove any carbon oxides before the separation step. 7. The process according to claim 1 ', characterized in that the nitrogen-rich stream is mixed with additive fuel and fed as fuel to the combustion chamber of a gas turbine. 8. A method according to claim 7, characterized in that the process air requirement for the partial oxidation is deducted from the gas turbine compressor output. 9. A process according to claim 1, characterized in that the stoichiometric excess of nitrogen is 230 - 270 mol%, based on the amount required for ammonia synthesis.