CN102079685B - Coal gasification process for methane preparation by two stage gasification stove - Google Patents

Abstract

The invention relates to a coal gasification process for methane preparation, including the following steps that: a. coal is reacted with oxygen containing gas in a first stage gasification stove to produce coal-gasified gas products containing CO, CO2, H2 and H2O; b. a coolant is fed to the coal-gasified gas products for cooling, and a first stage gas product is obtained; and c. the first stage gas product is fed to a second stage gasification stove and reacted with coal and a catalyst to form a second stage gas product containing methane.

Description

Method for producing methane by gasifying coal in two-stage gasifier

field of invention

The invention relates to a method for producing methane by gasification of coal, more specifically, the invention relates to a method for producing methane by gasification of coal in a two-stage gasifier.

Background technique

With the depletion of the world's oil resources and the demand for environmental protection in the sustainable development of human beings, the clean coal utilization technology represented by coal gasification will play an irreplaceable role in the future fossil energy. In particular, my country is rich in coal and poor in oil, and its coal storage ranks third in the world, and the geographical distribution of coal resources is uneven. The rational development and utilization of coal gasification technology has long-term strategic significance for ensuring China's energy security and economic development. Compared with existing natural gas, synthetic methane has attracted more and more industrialization attention due to its low cost and abundant (coal) raw material sources.

The current methanation technology can be roughly divided into two-step method (indirect method) and one-step method (direct method). The two-step method refers to the use of existing mature technologies (such as German entrained bed or Lurgi furnace technology) to gasify coal or coal water slurry into products such as _H2 and CO with air or oxygen and other oxidants, and the product gas is cooled After purification processes such as acid gas removal (such as H ₂ S, etc.), and removal of entrained particles, the H/C ratio is adjusted through the water-gas shift reaction, and finally methane is synthesized under the action of nickel-based or other catalysts. The advantage of the two-step method is that the two-step process of gasification and methanation is operated separately, and the technology is relatively mature, such as the synthetic methane technology (SNG) of Great Plains. The disadvantage is that the synthesis gas needs to add expensive and complicated purification equipment, the cost is relatively high, and the overall thermal efficiency of the process is low due to the introduction of synthesis gas purification and water-gas shift devices. The two-step method that has been officially put into production is only the technology of Great Plains, and the others are relatively immature.

The one-step method is to directly react and gasify coal and water vapor into methane under the action of a catalyst (usually an alkali metal catalyst). Under the funding of the U.S. Department of Energy, Exxon conducted a large number of research work on coal catalytic gasification in the 1970s and 1980s. The general process of the process is to flow superheated steam and coal mixed with catalyst Catalytic gasification reaction is carried out in the bed to directly synthesize methane. In addition to coal, substances containing high fixed carbon such as petroleum coke can also use similar processes. For example, US2007/0083072 proposes a process for catalytic gasification of petroleum residues. Compared with the two-step method, the one-step method has the advantages of simple process and high thermal efficiency. The disadvantage is that it is necessary to provide additional equipment for preparing high-temperature (800-900°C) superheated steam and insulation devices to provide the heat required for oxygen-free oxidation and to compensate for the heat loss caused by system heat dissipation.

The reaction of coal and water to generate methane is a slightly endothermic reaction, as shown in the reaction formula (1):

C+H ₂ O→CH ₄ +CO ₂ 5.4KJ/mol (1)

In theory, only a small amount of heat needs to be added to maintain the energy loss caused by system heat dissipation. However, the gasification process is accompanied by parallel reactions such as the gasification reaction of water vapor and coal (reaction equation (2)) and the water gas shift reaction (reaction equation (3)), in which the gasification reaction of water vapor and coal (reaction equation ( 2)) is a strong endothermic reaction, and the reaction degree is relatively large, so more heat is required to maintain the constant temperature gasification reaction in actual operation.

C+H ₂ O→H ₂ +CO 131KJ/mol (2)

CO+H ₂ O→CO ₂ +H ₂ -41KJ/mol (3)

The traditional way to maintain a suitable catalytic gasification temperature (~700°C) is to use a higher inlet temperature of water vapor (800~900°C), such as Exxon's coal catalytic gasification technology, see for example HA Marshall and FCRMSmits, "Exxon catalytic coal gasification coal gasification process and large pilot plant development program, "Pittsburgh, PA, USA, 1982, pp. 357-377. The preparation of superheated steam at 800-900 °C usually requires multi-stage superheaters and high-power boilers, resulting in high total energy consumption of the system. In addition, during the heating process of water vapor from saturated water vapor to superheated steam, there is a problem of material corrosion under high temperature and high pressure, so higher requirements are put forward for the materials of equipment for producing and transporting superheated steam. The patent US4292048 using a one-step method proposes a method of methane reforming, that is, the CO and H ₂ generated by the reaction of CH ₄ and H ₂ O and the CO and H ₂ separated from the gasifier are passed into the gasifier to increase methane yield and make the reaction close to thermoneutrality, thereby reducing the heat required for endothermic reactions (mainly reaction formula (2)). The disadvantage of this method is that the required CO and _H2 circulation is relatively large, which increases the system energy consumption and equipment size.

Summary of the invention

The invention provides a method for coal gasification to generate methane, comprising the following steps:

a. Make coal and oxygen-containing gas react in the primary gasifier to generate coal gasification gas products including CO, CO ₂ , H ₂ , and H ₂ O;

b. Passing a coolant into the coal gasification gas product to lower the temperature to obtain a first-grade gas product;

c. passing the primary gas product into a secondary gasifier and reacting with coal and a catalyst to obtain a secondary gas product containing methane.

Brief description of the drawings

Figure 1 is a flow diagram of one embodiment of the process of the present invention.

Figure 2 is a schematic diagram of a primary gasifier used in the process of the present invention.

Fig. 3 is a schematic diagram of a secondary gasification furnace used in the method of the present invention, wherein Fig. 3A is a front view of the furnace, and Fig. 3B is a top view of the interior of the furnace.

These figures are merely illustrative and do not limit the scope of the invention in any way.

Detailed description of the invention

The process of the invention is carried out in two-stage gasifiers connected in series. The present invention will be described in detail below in conjunction with FIG. 1 .

In step a of the present invention, coal and oxygen-containing gas are reacted in a primary gasifier to generate coal gasification gas products including CO, CO ₂ , H ₂ , and H ₂ O. Wherein the coal can be passed into the primary gasifier in the form of coal-water slurry or dry coal powder, and the feed equipment is conventional slurry feed equipment in the field such as high-pressure coal-water slurry delivery pump (such as diaphragm pump) and coal-water Slurry nozzles or solid feeding equipment such as lock hopper feeding and pressurized blowing equipment. At the same time, oxygen-containing gas is fed into the primary gasifier, and the oxygen-containing gas can be air, oxygen-enriched air or pure oxygen. Coal and oxygen undergo a gasification reaction at a temperature of 900-1600°C and a pressure of 20-70atm (referring to absolute pressure, the same below) in the primary gasifier to produce CO, CO ₂ , H ₂ , H ₂ O The coal gasification gas product, if air or oxygen-enriched air is used, the coal gasification gas product also includes nitrogen and inert gases. The gasification reaction of coal and oxygen releases a large amount of heat, part of which is used to maintain the high temperature of the primary gasifier, and the other part is stored in the coal gasification gas product for later use. The coal gasification gas product moves upward along the primary gasifier, and the ash generated after gasification is discharged from the bottom of the primary gasifier.

In step b of the present invention, a coolant is passed into the coal gasification gas product to lower the temperature to obtain a primary gas product. The purpose of passing through the coolant to lower the temperature is to adjust the temperature of the gas to be slightly higher than the temperature at which the catalyst of the secondary gasification furnace is suitable for catalytic action. Wherein the coolant is liquid water or water vapor at a temperature of 200-350° C. or CO and H ₂ separated and recycled from the gas separation process after the two-stage gasification furnace process of the present invention, or their mixture. In embodiments operating with mixtures of these, the coolant is primarily water or steam, with recirculated CO and _H2 acting as auxiliary cooling, the main purpose of circulating CO and _H2 is to increase the CH ₄ yield. As the name implies, these coolants should be at a lower temperature than the coal gasification gas products. When the coolant is liquid water or low-temperature water vapor, the gas phase composition of the coal gasification gas product will change due to the existence of the water-gas shift reaction (see Equation 3 above); when the coolant is recycled CO and _H2 , the coal gas The gas phase composition of the gasification gas product will also change accordingly. The gaseous product whose gaseous phase composition changes due to cooling by adding coolant is called primary gaseous product. Wherein the coolant can be introduced at any position between the middle of the primary gasifier and the outlet of the primary gasifier, for example through at least one channel between the middle of the primary gasifier and the outlet of the primary gasifier The nozzles, which are preferably arranged in the opposite position, lead into the primary gasifier. Alternatively, the coolant can also be passed into the connecting pipe between the primary gasifier and the secondary gasifier. Alternatively, it is possible to introduce cooling gas at any position between the middle of the primary gasifier and the outlet of the primary gasifier and in the connecting pipe between the primary gasifier and the secondary gasifier. agent to achieve step b. The temperature of the primary gas product formed after cooling is 800-900°C.

In step c of the present invention, the primary gas product is passed into a secondary gasifier and reacted with coal and a catalyst to obtain a secondary gas product containing methane. Wherein, the temperature in the secondary gasifier is 650-750° C., the pressure is 20-40 atm, and the heat required to maintain the temperature in the secondary gasifier can be completely or partially provided by the primary gas product. The catalyst used in this step c is selected from alkali metal carbonates or alkali metal hydroxides or their mixtures. The coal and the catalyst can be passed into the secondary gasifier separately or in the form of a mixture, preferably in the form of a mixture, wherein the coal and The aqueous catalyst solutions are mixed together and dried to obtain a mixture of coal and catalyst. The feeding equipment adopted is also a conventional feeding equipment in the art, such as a lock bucket feeding device and the like. According to the water-to-coal ratio required for fluidization and catalytic gasification in the secondary gasifier, it is preferable to additionally feed superheated steam into the secondary gasifier to assist in maintaining the fluidized state and Improve the conversion rate of coal gasification. The temperature of the superheated steam is 800-900°C, and the pressure is 20-40atm, which can be directly passed into the secondary gasifier or into the connecting pipe between the primary gasifier and the secondary gasifier Among them, it is preferred to directly pass into the secondary gasifier, for example, enter the secondary gasifier through a conical distribution plate located at the bottom of the secondary gasifier. Under the action of the catalyst, the pulverized coal reacts with the primary gas product as shown in the following equation to generate secondary gas products including methane. The secondary gas product leaves the secondary gasifier and enters the subsequent gas separation process , while the ash generated in the secondary gasifier is discharged from the bottom of the secondary gasifier.

C+ _H2O → _H2 +CO (4)

CO+ _H2O → _CO2 + _H2 (3)

3H ₂ +CO→CH ₄ +H ₂ O (5)

Secondary gas products are separated from CO, H ₂ , CO ₂ , etc. by conventional separation means in the field in the subsequent gas separation process, and finally high-purity methane gas is obtained. These separation means are well known to those skilled in the art and will not be repeated here repeat. Gases such as CO and H ₂ separated in the separation process can be used as coolant alone, or as a supplement to other coolants such as liquid water or low-temperature water vapor to implement step b.

The ash discharged from the secondary gasifier contains semi-coke, ash and catalysts. The catalyst can be separated and recovered by conventional separation means in the art, and the recovered catalyst can be recycled. These are well known to those skilled in the art and will not be repeated here.

The primary gasifier used in the method of the present invention may be an entrained bed, a fluidized bed or a conveyed bed. The example of entrained flow bed can be several types such as the egas entrained bed of Shell, GE or ConocoPhilips company; The example of fluidized bed can be ugas fluidized bed, also can be KRW ash fusion fluidized bed; conveyor gasifier, etc. When these gasifiers are directly used without any modification, coolant needs to be introduced into the connecting pipes between the primary gasifier and the secondary gasifier. As a preferred embodiment of the present invention, the various gasifiers mentioned above can be modified. The modification refers to the addition of coolant nozzles before the outlets of these gasifiers, preferably at least one pair of nozzles placed in opposite positions, through These nozzles feed coolant into the primary gasifier to quench the coal gasification gas product. Wherein the specific structure of the egas entrained bed of Shell, GE or ConocoPhilips without transformation is respectively referring to the following references:

Schuurman, P.J. US Patent 4202672 entitled "Apparatus for gasification of finelydivided fuel";

Schlinger, W.G. "Coal gasification development and commercialization of the Texaco coal gasification process", International Journal of Energy Research, 2007, vol 4(2), 127-136; and

Rotter, Franz US Patent 4,306,506 entitled "Gasification apparatus";

Examples of conveyor beds are found in the following references:

Brandon M. Davis, Roxann Leonard, P. Vimalchand, Guohai Liu, Peter V. Smith, Ron Breault, "Operation of the PSDF transportgasifier", Twenty-second Annual Pittsburgh Coal Conference, Pittsburgh, PA, September 12-15, 2005.

For uga s fluidized bed and KRW ash fusion fluidized bed, see the following references:

Jequier, J., Longchambon, L., and Van De Putte, G., "The gasification of coal fines", J. Inst. Fuel, 1960, 33584-591, and

Hartman, H.F., Belk, J.P., Reagan, E.E., Low Btu coalgasification processes, vol 2, Selected Process Descriptions, 1978, 11, A-139-151;

The contents of these patents or papers are incorporated herein by reference.

Fig. 2 shows an example of the modified egas entrained bed as a primary gasifier. Fig. 2 only shows the feeding conditions of each material, and omits the specific internal structure of the gasifier. The coal water slurry and oxygen are mixed and enter the bottom of the primary gasifier, where the gasification reaction occurs in the high temperature (1400-1500°C) zone at the bottom of the primary gasifier. Different from the original coal-water slurry swirling feeding method at the second stage of egas, at any position before the exit of the first-stage gasifier, there are at least one pair of nozzles placed in opposite positions, through which the coolant Passed into the first-stage gasifier, this counter-positioning method strengthens the mixing of coal gasification gas products and coolant, thereby realizing rapid cooling.

The secondary gasifier used in the method of the present invention may be a fluidized bed or a circulating fluidized bed, but a fluidized bed is preferred. Since the coal gasification gas product and the primary gas product have not been dedusted, the primary gas product entering the secondary gasifier is often entrained with coal ash or incompletely reacted coal char particles. In order to prevent the entrained particles from clogging the secondary The gas distribution plate of the gasifier, the secondary gasifier preferably adopts the jet bed operation mode. Jet-fluidized bed, also known as jet-fluidized bed, is a bed type composed of high-speed (vertical, horizontal or inclined) jets sprayed into a fluidized bed in a limited space. In practical application, it is common that the high-speed vertical jet fluid enters the bed through the conical distribution plate at the bottom or the flat-bottom nozzle or plug-in nozzle in the center of the flat-bottom distribution plate to form two flow states in which jet flow and fluidization coexist at the same time. See the following two references for details on the structure and operation of a fluidized bed:

Jequier, J., Longchambon, L., and Van De Putte, G., "The gasification of coal fines", J. Inst. Fuel, 1960, 33584-591, and

Hartman, H.F., Belk, J.P., Reagan, E.E., Low Btu coalgasification processes, vol 2, Selected Process Descriptions, 1978, 11, A-139-151;

These references are incorporated herein by reference in their entirety. Figure 3 shows a diagram of a jet bed: the primary gas product is injected into the bed from the center tube of the jet bed, which not only avoids entrained particles from clogging the gas distribution plate, but also can be adjusted by adjusting the diameter of the center tube and the inlet flow rate. Realize the separation of ash and coke with different densities. The fluidized water vapor is introduced from the bottom, and the coal and catalyst are introduced from a certain position in the middle of the secondary gasifier.

Those skilled in the art will understand that the present invention is not only applicable to coal, but can be extended to various carbonaceous materials, such as petroleum coke and the like. Among them, petroleum coke refers to the product obtained by separating light oil and heavy oil through distillation of crude oil, and then converting the heavy oil through thermal cracking process. The main component element is carbon, which accounts for more than 80 wt%, For hydrogen, oxygen, nitrogen, sulfur and metal elements.

The advantages of the present invention are as follows:

(1) In this process, the high-temperature gas produced by the primary gasifier can be directly used in the secondary gasifier after temperature adjustment, providing the reaction heat required for the reaction of the secondary gasifier, and reducing the pressure of the secondary catalytic gasification. The load of the superheated steam boiler, the overall thermal efficiency is higher than the traditional two-step methane process.

(2) There is no need to add separate purification equipment to remove CO ₂ , H ₂ S or entrained particles before the gas enters the secondary gasifier, which reduces equipment investment.

(3) The synthesis gas rich in CO and H ₂ (60-80 vol%) produced by the primary gasifier can effectively increase the methane yield of catalytic gasification of the secondary gasifier, compared with the one-step methanation process The amount of CO and _H2 circulation is alleviated, thereby reducing energy consumption.

Claims (11)

1. gasification generates a method for methane, comprises the following steps:

A. make coal and oxygen-containing gas is that 900-1600 ℃ of pressure is generating gasification reaction under 20-70atm in temperature in one-level vapourizing furnace, generates and comprises CO, CO ₂, H ₂, H ₂the gasification gaseous product of O; Described oxygen-containing gas is air, oxygen-rich air or purity oxygen;

B. to passing into refrigerant in described gasification gaseous product, lower the temperature, obtain one-level gaseous product; The temperature of described one-level gaseous product is 800-900 ℃; Described refrigerant is CO and the H of recirculation ₂;

C. described one-level gaseous product being passed in secondary vapourizing furnace and with coal and catalyzer is that 650～750 ℃ of pressure are to react under 20-40atm in temperature, obtains the secondary gas product that comprises methane; Described catalyzer is selected from alkaline carbonate or basic metal oxygen oxide compound or their mixture.

2. the process of claim 1 wherein that coal in step a passes in one-level vapourizing furnace with the form of coal water slurry or dry coal dust.

3. the process of claim 1 wherein that by the middle part at one-level vapourizing furnace, to any position between the outlet of one-level vapourizing furnace, passing into described refrigerant carrys out performing step b.

4. the method for claim 3, the nozzle of wherein laying at least one pair of contraposition between the outlet of one-level vapourizing furnace by the middle part at one-level vapourizing furnace passes into refrigerant in one-level vapourizing furnace.

5. the process of claim 1 wherein and carry out performing step b by passing into described refrigerant in the connecting tube between one-level vapourizing furnace and secondary vapourizing furnace.

6. the process of claim 1 wherein and to all passing into refrigerant in any position between one-level vapourizing furnace outlet and the connecting tube between one-level vapourizing furnace and secondary vapourizing furnace, carry out performing step b by the middle part at one-level vapourizing furnace.

7. the process of claim 1 wherein that coal in step c and catalyzer pass into respectively in secondary vapourizing furnace or pass in secondary vapourizing furnace with the form of mixture.

8. the method for claim 3, wherein said one-level vapourizing furnace is air flow bed, fluidized-bed or carries bed, wherein before the outlet of this one-level vapourizing furnace, sets up coolant jet.

9. the method for claim 5, wherein said one-level vapourizing furnace is air flow bed, fluidized-bed or carries bed, before the outlet of this one-level vapourizing furnace, sets up coolant jet.

10. the process of claim 1 wherein that described secondary vapourizing furnace is jet-flow bed.

The method of 11. claims 1, also comprises described secondary gas product is carried out to gas delivery to obtain the step of methane.

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