How to choose the gasification process in the ammonia process technology solution?

Gasification processes are generally divided into three types: fixed bed, fluidized bed and fluid bed.

1.Fixed Bed Gasification

Gasification of coal in fixed-bed gasifier, also known as lump coal gasification. It is also called lump coal gasification. It includes two types of fixed-bed gasification technology: atmospheric pressure fixed-bed gasification and pressurized fixed-bed gasification, and the gasification technology belonging to this type includes Lurgi gasification, UGI coal gasification and oxygen-enriched continuous gasification.

2.Fluidized Bed Gasification

Fluidized bed gasification of coal means that the gasification reaction is carried out in the fluidized bed formed by gasifier and coal. Fluidized bed gasifier adopts crushed coal as raw material, and uses oxidant (oxygen or air) to fluidize the bed, and its temperature is kept below 1000℃ to prevent the agglomeration of ash melting and the material in the bed. Fluidized bed gasification technology mainly includes Win Kier, High Temperature Win Kier, U-Gas, Endeavour Furnace, Ash Fusion and other fluidized bed pulverized coal gasification technologies.

3.Air-flow bed gasification technology

Air-flow bed gasifier belongs to the third generation of advanced coal gasification technology, which is the cleanest and most efficient type of coal gasification. The pulverized coal (water slurry) is partially oxidized at 1200-1700°C. The high temperature ensures complete gasification of the coal, and the minerals in the coal become slag and leave the gasifier. The range of coal types used in gas-flow beds is wider than that of fixed and fluidized beds. The use of oxygen makes the gasification more efficient and prevents the syngas from being diluted by nitrogen. The calorific value of the syngas is also higher than that of the syngas produced in air gasifiers.

Typical examples of current fluidized bed gasification processes for the production of syngas from coal are:

Texaco coal-water slurry pressurized gasification process.

Shell (SHELL) dry pulverized coal pressurized gasification process (SCGP).

Germany's future energy company's GSP, or Colin company dry pulverized coal pressurized gasification process; domestic new opposing multi-nozzle coal water slurry pressurized gasification; coal as raw material gasification process is the key is based on the type of coal and the production scale of the selection of a good gasifier. According to the preliminary coal quality analysis provided so far, the coal has high activity and high ash content, although it is suitable for gasification, but it is necessary to choose the technology suitable for gasification of this coal. According to the analysis of coal quality, the gasification technologies that can be considered are Dutch SHELL, German GSP, German Ruchi and GTI circulating fluidized bed gasification technology.

(1) Holland SHELL, this technology is an advanced coal gasification technology developed in recent years, and there are only industrialized plants in China. China has contracted to introduce 19 sets of this technology, of which five sets have been put into operation and are currently in trial operation. The scale of this technology is large, a furnace can meet the needs of 300,000 tons of ammonia synthesis, the carbon conversion rate can reach more than 98%, but the technology has high investment, high requirements for coal moisture, coal needs to be dried.

Advantages: wide adaptation of coal, high thermal efficiency of carbon conversion rate, high quality of synthesized gas, long service life of the device, green and environmental protection.

Disadvantages: There is no lignite coal performance at present, and the requirement of coal moisture is high. Gasifier and waste heat boiler have complex structure and great difficulty in manufacturing, and its internal parts and key equipments still need to be introduced; for the same scale of production, the investment is relatively large; there are 5 gasifiers in China which have just been put into operation, but the driving is unstable, and there is a lack of successful operation and management and operation experience.

(2) Germany GSP, the technology is introduced to be more advanced, at present China has several sets of contracted introduction, but there is no industrialized coal gasification plant. Its investment is slightly lower than the Dutch SHELL.

The technology was developed in 1976 by the former GDR VEB Blackwater Pump Company, in 1979 the former GDR Institute of Fuel Research in Freiburg built a heat load 3MW spoon pilot plant, in 1984 in the city of Blackwater Pump built a heat load 130MW gasification demonstration device, the daily coal input 720 tons / day lignite, gas production of 50,000mVH, the gasification pressure of 2.8MPA temperature of 1400 C. The gasification of coal gasification, the gasification pressure is 2.8MPA operating temperature of 1400 C, the gasification of coal gasification of the GSP, the technology is more advanced. The gasification pressure is 2.8MPA and the operating temperature is 1400 C.

Advantages: lower water injection cooling to reduce equipment costs, the conversion does not need to make up water steam Disadvantages: there are only two sets of demonstration units in operation, less operational experience (single furnace 720t/d lignite, operating temperature of 1400 C, there is no experience in gasification of high ash and high ash melting point coal), the gasifier is small in height to diameter ratio and the single nozzle design so that the scale of the enlargement of the limitations.

(3) GTI Circulating Fluidized Bed Gasification Technology

GTI circulating fluidized bed gasification technology comes from the Gas Technology Institute (GTI) in the United States, which developed the technology based on its major technology research project on "substituting imported petroleum with domestic solid fuels". The technology was successful in the 1970s and was used in large-scale industrial production by the 1990s, and SES has an exclusive license for GTI vaporization technology in Asia. The advantage of this technology is the ability to use low-cost waste coal and other "low-value" hydrocarbons as fuel, which are difficult to adapt to other types of gasifiers.

The fluidized bed gasifier gasification process is a non-catalytic, continuous feed, partial oxidation process in a circulating fluidized bed ash agglomeration mode. Partial oxidation is the raw material - coal spoon gasification process, the oxidant - that is, pure oxygen (oxygen-rich) and temperature regulator - steam, through the gasifier feed nozzle into the gasifier chamber, in the high temperature and high pressure and oxygen, and then the gasification process is carried out. Under high temperature, high pressure and insufficient oxygen for complete combustion, the carbon in the fuel is mainly converted into carbon monoxide, a small part of which is completely oxidized to carbon dioxide. Hydrogen in the fuel is mainly converted into hydrogen. The sulphur in the fuel is mainly converted to hydrogen sulphide (H2S), with a small portion converted to carbonyl sulphide (COS). Since the gasifier operates in a highly reducing atmosphere, neither nitrogen nor sulfur can be oxidized to nitrogen oxides (NOx) or sulfur oxides (SOx).

Circulating fluidized bed technology is a technology that is receiving increasing attention spoon because:

1) Ash limit is small. Whether it is coal-water slurry gasification process or dry pulverized coal gasification process, the ash content is required to be less than 12%. Practice has proved that the ash is too high, under high temperature and pressure conditions, oxygen and coal spoon consumption grows very quickly, very uneconomical; while the circulating fluidized bed is a linear increase, the growth is not very large.

2) Simple process, less investment.

3) Short construction period. As the gasification process at atmospheric pressure or low pressure conditions, equipment manufacturing is relatively easy, investment, short cycle, the construction period is generally only about one year.

4) Ruchi gasification technology

This technology is mature, and is used by three companies in China, mainly for city gas. Due to the complicated operation, low gasification temperature, high tar content, difficult tar recovery and high pressure on environmental protection, the scale of this technology is small, and it needs to be imported with high investment, and it has not been imported in China for many years, therefore, this technology is not considered in this comparison.