CN107325846B - Coal pyrolysis chemical looping gasification coupling process based on low-rank coal cascade utilization - Google Patents

Abstract

A coal pyrolysis chemical chain gasification coupling process based on the cascade utilization of low-rank coal. Coal pyrolysis produces coal tar, coal gas and semi-coke, and the semi-coke is used in the chemical chain gasification process for the purpose of producing synthesis gas. The chemical looping gasification process uses Fe ₂ O ₃ as an oxygen carrier to react with semi-coke in the gasification reactor to obtain syngas mainly composed of CO and H ₂ and iron oxides mainly composed of FeO/Fe. As the solid heat carrier of coal pyrolysis, iron oxide enters the coal pyrolysis reactor to generate corresponding pyrolysis products. The separated FeO/Fe and the FeO/Fe in the gasification reactor re-enter the oxygen carrier regeneration reactor to undergo redox reaction with air to obtain high-valent iron oxide Fe ₂ O ₃ and release heat at the same time. The material circulation of iron oxide in each reactor realizes the heat transfer of each operation unit, and the organic coupling of coal pyrolysis and chemical chain gasification improves the utilization efficiency of coal, reduces energy consumption, and realizes the cascade utilization of low-rank coal.

Description

Coal pyrolysis chemical looping gasification coupling process based on low-rank coal cascade utilization

technical field

The invention relates to a low-rank coal cascade utilization polygeneration process, which can be used in the technical field of comprehensive and efficient utilization of low-quality coal such as lignite, and in particular relates to a process for co-producing coal gas, tar and sponge iron by low-temperature dry distillation and chemical chain gasification of lignite.

Background technique

Chemical looping gasification is to use the lattice oxygen in the oxygen carrier to replace the gasification medium such as oxygen-enriched air in the conventional gasification reaction, to provide the required oxygen elements for solid fuel gasification, and to obtain CO and _H2 -based syngas. Compared with the traditional gasification method, it has the following advantages: it saves the equipment for preparing pure oxygen and saves cost; the oxidation of oxygen carrier is an exothermic reaction, which can provide heat for the subsequent process and play the role of heat carrier.

Coal pyrolysis is to heat lignite and high volatile bituminous coal in an inert atmosphere to produce semi-coke, gas, tar and other products. Compared with the gasification or liquefaction process, coal pyrolysis has the advantages of simple process, mild conditions and low production cost. In recent years, the solid heat carrier coal pyrolysis process based on circulating fluidized bed is one of the best methods for comprehensive utilization of coal resources. It has the advantages of strong applicability of coal types, clean and efficient, and desulfurization in the furnace. It can also efficiently burn low-quality coal , the stable high-temperature hot ash circulating flow in the furnace can carry a large amount of heat that can be used outside the furnace.

my country has abundant coal resources, and the efficient, clean and sustainable utilization of coal resources has always been a difficult problem in coal utilization. Coal low-temperature pyrolysis technology can obtain pyrolysis semi-coke while obtaining coal tar and pyrolysis gas, and pyrolysis semi-coke continues the characteristics of high activity and reactivity of coal. At present, most of the research focuses on a single independent system, and there are few applied research on the coupling of chemical looping gasification and coal low-temperature pyrolysis process. If the coal low-temperature pyrolysis process and the coal gas chemical looping gasification process are considered as a system, that is, the polygeneration system of coal. In terms of overall utilization efficiency, it can improve the utilization rate of coal resources and realize the cascade utilization of low-rank coal. In addition, the temperature gradient of each reaction system can also be used to realize heat transfer through the material circulation of the oxygen carrier, which greatly improves the utilization rate of energy.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the existing lignite polygeneration technology, to provide a polygeneration process based on low-temperature coal pyrolysis and coal-based chemical chain gasification, which can obtain coal tar with higher added value and simultaneously Synthesis gas mainly composed of CO and _H2 can be obtained as a raw material for the synthesis of LNG (liquefied natural gas). Thus, the cascade utilization of low-rank coal is realized, and the temperature gradient of each reaction system is used to realize the heat transfer through the material circulation of the oxygen carrier, which greatly improves the utilization rate of energy. In addition, if iron ore is used as an oxygen carrier to participate in the gasification reaction of pyrolysis semi-coke in the gasification reaction system, the highly active reduced iron oxides of pyrolysis semi-coke can be used to prepare sponge iron, realizing the comprehensive utilization of various substances . The gas generated by coal pyrolysis is recycled, which not only saves energy, but also strengthens the reducing atmosphere.

Technical scheme of the present invention:

A coal pyrolysis chemical chain gasification coupling process based on the cascade utilization of low-rank coal, including a pyrolysis reaction system, a gasification reaction system for semi-coke gasification, and an oxygen carrier regeneration reaction system for oxygen carrier oxidation. Raw material pretreatment system for crushing, screening and drying, and product treatment system for product separation and condensation;

1) The raw coal is crushed and sieved to the required particle size in the crushing and screening device, and after being preheated and dried, it enters the pyrolysis reaction system and the low-valent iron oxide (as FeO/ Fe-based) mixed with pyrolysis reaction, the pyrolysis reaction temperature is 400 ℃ ~ 600 ℃; Among them, iron oxide is used as a solid heat carrier in the coal pyrolysis reaction system to provide the heat required for the reaction of coal pyrolysis, improving energy efficiency;

In the pyrolysis reaction system, the following reactions mainly occur: coal→semi-coke+raw coal gas;

The semi-coke produced by pyrolysis enters the gasification reaction system, and the raw coal gas generated is condensed by a heat exchanger to obtain liquid phase products and coal pyrolysis gas, and the liquid phase products are separated to obtain phenol waste water and tar, among which coal pyrolysis gas and phenol wastewater as the gasification medium of the gasification reaction system;

2) The semi-coke generated in the pyrolysis reaction system enters the gasification reaction system and mixes with the high-valence iron oxide (main component Fe ₂ O ₃ ) from the oxygen carrier regeneration reaction system, and the gasification reaction occurs. The temperature is 750 ℃ ~ 950 ℃; the temperature of iron oxide from the oxygen carrier regeneration reaction system is used as the gasification reaction system to provide the heat required for the reaction, and the energy utilization rate is improved; the compressed coal pyrolysis gas is used as the fluidization medium and participates in the reaction , the following reactions mainly take place:

Coal pyrolysis gas CO, H ₂ , CH ₄ : CO, H ₂ , CH ₄ +Fe ₂ O ₃ →Fe+FeO+CO ₂ +H ₂ O

Coke particle reduction: C+CO ₂ , H ₂ O→CO+H ₂

The low-valence iron oxides (mainly FeO/Fe) generated in the gasification reaction system enter the oxygen carrier regeneration reaction system to be oxidized again, and the generated syngas (mainly CO and H ₂ ) can also be used as The fluidized medium in the gasification reaction system is used to strengthen the reducing atmosphere of the fluidized bed gasification reaction system. While obtaining chemical products such as coal tar and syngas, it is also possible to adjust the operating parameters such as the circulation rate of syngas in the gasification reaction system, the ratio of coal/oxygen carrier, etc., so that Fe ₂ O ₃ can be reduced to Fe, so as to prepare sponge iron.

3) The low-valence iron oxides (mainly FeO/Fe) from the gasification reaction system and coal pyrolysis reaction system enter the oxygen carrier regeneration reaction system, and the low-valence state is made by controlling the feed amount of compressed air. The iron oxide is completely oxidized to Fe ₂ O ₃ and releases a lot of heat. The reaction temperature of the oxygen carrier regeneration reaction system is about 900°C-1100°C. The high-valence gas obtained after oxidation enters the gasification reaction system for the next cycle. The temperature gradient of the three reaction systems is used to transfer the lattice oxygen and heat at the same time by controlling the circulation of the oxygen carrier, so as to finally realize the self-heat balance of the entire reaction system and improve the energy utilization rate of the reaction system.

In the above technical scheme, part of the low-valence iron oxides generated in the gasification reaction system enters the coal pyrolysis reaction system, and serves as a solid heat carrier to provide the coal pyrolysis reaction system with the heat required for reaction, improving energy utilization. .

In the above technical scheme, the coal pyrolysis reaction system can be designed in the form of a fluidized bed, and the compressed coal pyrolysis gas or the synthesis gas produced by the gasification reaction system is used as the fluidization medium, and the pyrolysis semi-coke generated by pyrolysis enters the The gasification reaction system mixes and reacts with high-valence iron oxides from the oxygen carrier regeneration reaction system. High-valence iron oxides are used as oxygen carriers and heat carriers to provide lattice oxygen and required heat for semi-coke gasification, realizing the cascaded utilization of low-rank coal.

In the above technical solution, the gasification reaction system can be designed in the form of a fluidized bed, and the fluidized medium can be either the phenol wastewater and coal pyrolysis gas generated by the coal pyrolysis reaction system, or the synthesis gas generated in the gasification reaction system , and can control the feeding amount of fluidization gas to get the best process conditions.

In the above technical scheme, the oxygen carrier regeneration reaction system can be designed in the form of a fluidized bed, and the low-valence iron oxides in the gasification reaction system and coal pyrolysis reaction system enter the oxygen carrier regeneration reaction system and are compressed and oxidized by air. The high-valence iron oxide is recovered, and the recycling of the oxygen carrier is realized.

In the above technical scheme, the optimal process conditions can be obtained by controlling the operating parameters such as the oxygen carrier/coal ratio in the gasification reaction system, the fluidization gas/coal ratio, and the circulation amount of the oxygen carrier in the coal pyrolysis reaction system.

In the above technical scheme, the oxygen carriers used in the coupling process are not limited to iron oxides, oxides of other metals or nonmetals (such as Mn, Ni, Co, Cu, etc.) and salts (such as CaSO ₄ etc.) are used as the oxygen carrier of the coupling process.

Beneficial effects of the present invention: the present invention couples chemical looping gasification technology, coal solid heat carrier pyrolysis technology and circulating fluidized bed technology. It can also be recycled in iron oxide reduction, saving energy and strengthening the reducing atmosphere at the same time. The system has low requirements on the equipment of each process unit, simple production operation and good economic benefits.

Description of drawings

Figure 1 is a schematic diagram of the material and energy flow of a coal pyrolysis chemical looping gasification coupling process based on the cascade utilization of low-rank coal.

Fig. 2 is a flow chart of coal pyrolysis chemical looping gasification coupling process based on low-rank coal cascade utilization.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited to specific embodiments.

The above-mentioned system is used to implement the coal pyrolysis chemical chain gasification coupling process based on the cascade utilization of low-rank coal, and the percentages involved in the following examples are all mass percentages (%). The properties of the coal samples used in the experiment are shown in Table 1 and Table 2.

Table 1 Industrial analysis and elemental analysis of lignite

Note: * is obtained by subtraction method

Table 2 lignite low-temperature dry distillation experiment (20g aluminum retort method) wt/%, air-dry basis

Embodiment 1: The raw material used in this embodiment is lignite. The specific operation process flow chart is shown in Figure 2; the feed temperature of raw coal is 25°C. The raw coal is sent to the pyrolysis reaction system through the screw feeder after pretreatment operations such as crushing, screening, and drying, and is mixed with the low-valence iron oxide Me from the gasification reaction system for pyrolysis reaction to generate Raw coal gas is condensed to obtain tar and coal gas, of which the coal gas can be used as the fluidization medium of the gasification reaction system and coal pyrolysis reaction system, and the semi-coke produced by pyrolysis enters the gasification reaction system. The temperature in the pyrolysis reaction system is 460°C and normal pressure. The distribution of the pyrolysis reaction system product is shown in Table 3:

Table 3 Product distribution of pyrolysis reaction system

Pyrolysis semi-coke enters the gasification reaction system and mixes and reacts with high-valence iron oxide MeO (referring to Fe ₂ O ₃ in this example) from the oxygen carrier regeneration reaction system, and the compressed coal pyrolysis gas or synthesis gas As a fluidizing medium and participating in the reaction, the generated low-valence iron oxide Me enters the oxygen carrier regeneration reaction system to be oxidized again, and part of the syngas serves as the fluidizing medium in the gasification reaction system. The ratio of oxygen carrier MeO/coal is 7.5 (the mass ratio of the active component of oxygen carrier Fe ₂ O ₃ to the inert carrier Al ₂ O ₃ is 3:2), the circulation volume of syngas/coal ratio is 0.3, and the temperature is 700°C, normal pressure. The product distribution of the gasification reaction system is shown in Table 4 and Table 5:

Table 4 Oxygen carrier distribution in gasification reaction system

Table 5 Distribution of gas phase products in gasification reaction system

The low-valence iron oxide Me from the gasification reaction system and the coal pyrolysis reaction system enters the oxygen carrier regeneration reaction system, and passes through compressed air so that the low-valence iron oxide Me is completely oxidized to MeO and released Lots of heat. The air/oxygen carrier MeO ratio in the oxygen carrier regeneration reaction system is 0.6 (the volume fraction of N ₂ is 79%, and the volume fraction of O ₂ is 21%), the temperature is 900° C., and normal pressure. The product distribution of the oxygen carrier regeneration reaction system is shown in Table 6:

Table 6 Product distribution of oxygen carrier regeneration reaction system

Embodiment 2: The raw material used in this embodiment is lignite. The specific operation process flow chart is shown in Figure 2; the feed temperature of raw coal is 25°C. The raw coal is sent to the pyrolysis reaction system through the screw feeder after pretreatment operations such as crushing, screening, and drying, and is mixed with the low-valence iron oxide Me from the gasification reaction system for pyrolysis reaction to generate Raw coal gas is condensed to obtain tar and coal gas, of which the coal gas can be used as the fluidization medium of the gasification reaction system and coal pyrolysis reaction system, and the semi-coke produced by pyrolysis enters the gasification reaction system. The temperature in the pyrolysis reaction system is 500° C., and the pressure is 20 atm. The distribution of pyrolysis reaction system products is shown in Table 7:

Table 7 Pyrolysis reaction system product distribution

Pyrolysis semi-coke enters the gasification reaction system and mixes and reacts with high-valence iron oxide MeO ((in this example, Fe ₂ O ₃ )) from the oxygen carrier regeneration reaction system, and the compressed coal pyrolysis gas or The syngas acts as a fluidization medium and participates in the reaction, and the low-valence iron oxide Me produced enters the oxygen carrier regeneration reaction system to be oxidized again, and part of the syngas serves as the fluidization medium in the gasification reaction system. The ratio of oxygen carrier MeO/coal is 4.8 (the mass ratio of the active component of oxygen carrier Fe ₂ O ₃ to the inert carrier Al ₂ O ₃ is 3:2), the circulation volume of syngas/coal ratio is 0.2, and the temperature is 800°C, pressure 20atm. The product distribution of the gasification reaction system is shown in Table 8 and Table 9:

Table 8 Oxygen carrier distribution in gasification reaction system

Table 9 Distribution of gas phase products in gasification reaction system

The low-valence iron oxide Me from the gasification reaction system and the coal pyrolysis reaction system enters the oxygen carrier regeneration reaction system, and passes through the compressed air so that the low-valence iron oxide Me is completely oxidized to MeO and released Lots of heat. The air/oxygen carrier MeO ratio in the oxygen carrier regeneration reaction system is 1.0 (the volume fraction of N ₂ is 79%, and the volume fraction of O ₂ is 21%), the temperature is 1000° C., and the pressure is 20 atm. The product distribution of the oxygen carrier regeneration reaction system is shown in Table 10:

Table 10 Product distribution of oxygen carrier regeneration reaction system

Embodiment 3: The raw material used in this embodiment is lignite. The specific operation process flow chart is shown in Figure 2; the feed temperature of raw coal is 25°C. The raw coal is sent to the pyrolysis reaction system through the screw feeder after pretreatment operations such as crushing, screening, and drying, and is mixed with the low-valence iron oxide Me from the gasification reaction system for pyrolysis reaction to generate Raw coal gas is condensed to obtain tar and coal gas, of which the coal gas can be used as the fluidization medium of the gasification reaction system and coal pyrolysis reaction system, and the semi-coke produced by pyrolysis enters the gasification reaction system. The temperature in the pyrolysis reaction system is 580° C., and the pressure is 30 atm. The distribution of pyrolysis reaction system product is as shown in table 11:

Table 11 Pyrolysis reaction system product distribution

Pyrolysis semi-coke enters the gasification reaction system and mixes and reacts with high-valence iron oxide MeO ((in this example, Fe ₂ O ₃ )) from the oxygen carrier regeneration reaction system, and the compressed coal pyrolysis gas or The syngas acts as a fluidization medium and participates in the reaction, and the low-valence iron oxide Me produced enters the oxygen carrier regeneration reaction system to be oxidized again, and part of the syngas serves as the fluidization medium in the gasification reaction system. The ratio of oxygen carrier MeO/coal is 7.5 (the mass ratio of the active component of oxygen carrier Fe ₂ O ₃ to the inert carrier Al ₂ O ₃ is 3:2), the circulation volume of syngas/coal ratio is 0.3, and the temperature is 900°C, pressure 30atm. The product distribution of the gasification reaction system is shown in Table 12 and Table 13:

Table 12 Distribution of oxygen carrier in gasification reaction system

Table 13 Gasification reaction system gas phase product distribution

The low-valence iron oxide Me from the gasification reaction system and the coal pyrolysis reaction system enters the oxygen carrier regeneration reaction system, and passes through compressed air so that the low-valence iron oxide Me is completely oxidized to MeO and released Lots of heat. The air/oxygen carrier MeO ratio in the oxygen carrier regeneration reaction system is 0.84 (the volume fraction of N ₂ is 79%, and the volume fraction of O ₂ is 21%), the temperature is 1100° C., and the pressure is 30 atm. The product distribution of the oxygen carrier regeneration reaction system is shown in Table 14:

Table 14 Product distribution of oxygen carrier regeneration reaction system

Claims (2)

1. a kind of pyrolysis of coal chemical chain gasification coupling technique based on low-order coal cascade utilization, which is characterized in that the coal heat Solving chemical chain gasification coupling technique includes pyrolytic reaction system, the gasification reaction system of char Gasification, the oxygen carrier of oxygen carrier oxidating Body regenerative response system, the feedstock pre-processing system be crushed, sieved to raw material, dried and separates product, is cold Solidifying product processing system；

1) feed coal is crushed in crushing and screening device, is sized to required granularity, and after preheated drying, into pyrolytic reaction System is mixed with the lower valency ferriferous oxide in gasification reaction system based on FeO/Fe, and pyrolytic reaction occurs, and pyrolysis is anti- Answering temperature is 400 DEG C~600 DEG C；Wherein, ferriferous oxide is mentioned as the solid thermal carriers in pyrolysis of coal reaction system for pyrolysis of coal For reacting institute's calorific requirement, capacity usage ratio is improved；

It is main that following reaction: coal → semicoke+raw coke oven gas occurs in pyrolytic reaction system；

The semicoke that pyrolysis generates enters gasification reaction system, and the raw coke oven gas of generation obtains liquid phase production after heat exchanger condensation process Object and coal pyrolysis gas, liquid product obtain phenol waste water and tar after separation, and wherein coal pyrolysis gas and phenol waste water are as gasified reverse Answer the gasifying medium of system；

2) semicoke generated in pyrolytic reaction system enter gasification reaction system in the oxygen carrier regenerative response system with Fe₂O₃Based on high valence iron oxide mixing, occur gasification reaction, gasification reaction temperature be 750 DEG C~950 DEG C；From oxygen carrier Ferriferous oxide temperature in body regenerative response system provides reaction institute's calorific requirement as gasification reaction system, improves energy utilization Rate；The coal pyrolysis gas of compression is as fluidizing agent and participates in reacting, main that following reaction occurs:

Coal pyrolysis gas CO, H₂、CH₄: CO, H₂,CH₄+Fe₂O₃→Fe+FeO+CO₂+H₂O

Coke granule reduction: C+CO₂,H₂O→CO+H₂

The lower valency ferriferous oxide based on FeO/Fe generated in gasification reaction system enters oxygen carrier regenerative response system In be oxidized again, generation with CO and H₂Based on synthesis gas, part also be used as the fluidizing agent in gasification reaction system, Reinforce the reducing atmosphere of fluidized gasification reaction system；It is also adjusted in gasification reaction system simultaneously obtaining coal tar, synthesis gas The internal circulating load of synthesis gas, coal/oxygen carrier make Fe than operating parameter₂O₃It is reduced into Fe, sponge iron is prepared with this；

3) the lower valency ferriferous oxide in gasification reaction system and pyrolytic reaction system based on FeO/Fe enters oxygen carrier In body regenerative response system, the inlet amount by controlling compressed air makes the ferriferous oxide of lower valency be completely oxidized to Fe₂O₃ And release big calorimetric；900 DEG C~1100 DEG C of oxygen carrier regenerative response system response temperature；The high valence iron oxidation obtained after oxidation Object enters gasification reaction system again, carries out next circulation.

2. a kind of pyrolysis of coal chemical chain gasification coupling technique based on low-order coal cascade utilization according to claim 1, It is characterized in that, it is described with Fe₂O₃Based on high valence iron oxide replace with Mn, Ni, Co and/or Cu oxide and CaSO₄。