Discussion on the operation cycles of various processes in gasification technology
Thread Content
There are a variety of coal gasification processes available in China, each with its own advantages and disadvantages. Considering factors such as process maturity and operation cycle, which of the coal slurry gasification process, the Lurgi process, and the Shell process is more suitable for synthetic ammonia plants in China?
In my opinion, for producing syngas or water-coal slurry, Shell is the better choice； In terms of stable operation of the device, water-coal slurry is slightly better.
The SHELL process is preferable for ammonia synthesis, as it has a high nitrogen content in the syngas and thus requires less nitrogen addition; the water-coal slurry process is second best, but both involve high shift reactor loads； The Lurgi process is suitable for producing city gas (natural gas) due to the high methane content in the syngas
Water-coal slurry technology is relatively mature, but the nozzles need to be replaced after about two months, and the refractory bricks in certain areas also require inspection and replacement; thus, there are still limitations. Information on Lurgi reactors: The gas composition makes it easy to produce methanol; currently, more Lurgi reactors are being used in large fertilizer production projects. It must have many advantages, right? I’d like to ask.
The Shell process uses pure oxygen and steam for gasification; the gasification temperature for dry powder feed is 1400–1700°C, with a carbon conversion rate of 99%. Liquid slag is produced as a by-product. The gasification pressure cannot be too high. The gasifier has a complex and large structure, resulting in high design and patent costs. The delivery time for the gasifier is at least 18 months, and the degree of localization of key equipment is low. The water-coal slurry process involves pressurizing the water-coal slurry and injecting it into a gasifier, where it undergoes combustion and partial oxidation reactions with pure oxygen. The gasification temperature ranges from 1300 to 1400°C. The gasifier has no moving parts, resulting in a low content of inert gases in the syngas. The gasification pressure is high, which reduces the energy required for compressing the syngas. It is adaptable to various types of coal, offers high raw material utilization efficiency, and is suitable for ammonia synthesis. The Ruchi furnace operates at a relatively low gasification temperature (~1000°C), resulting in a high methane content in the generated gas. Additionally, the gas contains various difficult-to-treat substances such as benzene, phenols, and tar; thus, the purification process is lengthy. Only lump coal can be used, not pulverized coal, which leads to low utilization of raw materials. Moreover, the treatment of waste gases, wastewater, and solid waste poses significant challenges.
Shell not only requires large investments, has a short operation cycle and high operating costs; Texaco’s operation cycle is fairly good, but its consumption levels are also high, and it has strict requirements regarding the type of coal used. It is said that domestically produced four-nozzle and HT-L furnaces perform quite well.
I studied it; I spent a whole day looking for information
Compared to the single-nozzle Texaco furnace, domestic four-nozzle gasification furnaces offer a higher carbon conversion rate and better production continuity (as only one pair of burners is required). Water-coal slurry is safer than pulverized coal, but it requires more valves and instruments, resulting in higher costs for related accessories. The Texaco single-nozzle furnace does not possess independent intellectual property rights, which means high patent fees; however, it requires fewer accessories and is easier to maintain. Both types of furnaces are widely used in China, and the choice depends on the products to be produced and the specific requirements of each facility.
The longest operating cycle for the Texaco gasifier has reached 197 days, while the operating cycle for the Huali four-nozzle technology has reached 104 days. Both technologies are well-developed; the consumption of the four-nozzle system is relatively low, and the coal conversion rate exceeds 97%.
I wonder where upstairs a Texaco furnace can have an operating cycle of over 197 days – that’s impressive. . .
You mentioned that the four-nozzle furnace at Huali University had an operation cycle of 104 days – was that the time observed during the pilot-scale testing of this process?