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Answer on October 29, 219
Abstract: The slag discharge system of biomass fixed bed gasifier is a very important system in biomass gasification. An effective slag discharge system can not only recover carbon slag quickly, but also save manpower and material resources. Based on the existing traditional slag discharge methods, an economical and effective slag discharge method is proposed.
classification number TK6
bioenergy belongs to new energy and renewable energy, and it is also a kind of clean energy. The development of bioenergy can reduce the dependence on traditional energy sources such as oil, natural gas and coal, which is of great significance to improving the environment and realizing the strategic goal of sustainable development, and is an industry strongly supported by the state. Biomass gasification is one of the ways to obtain biomass energy. Fixed bed gasifier is one of the most commonly used furnaces for biomass gasification. As one of the main systems of biomass gasification, the effectiveness and reliability of slag discharge system directly restricts the scale and industrialization of biomass gasification. Therefore, an economical and reliable slag tapping system is particularly important.
1 Basic requirements for slag discharge of fixed-bed gasifier
Fixed-bed gasification is a process of pyrolysis, oxidation, reduction and reforming of high polymers in biomass volatiles, thermal cracking or catalytic cracking into small molecular compounds and obtaining combustible gases containing CO, H2 and CH4 with the help of partial air (or oxygen) and steam. The ash produced after biomass gasification mainly contains a large amount of charcoal and a small amount of slag, and the slag tapping temperature is between 2℃ and 3℃. The high-temperature ash will burn violently immediately when it meets air, and the excess oxygen will explode when it contacts with gas. Therefore, the slag tapping of the fixed-bed gasifier is carried out under the condition of air isolation, and a large amount of air is not allowed to enter the fixed-bed gasifier during the slag tapping process.
2 Principle and characteristics of traditional slag discharging method
In coal gasification, the chain slag scraper is often used to discharge slag, and the slag hopper of the fixed bed gasifier directly extends to the box body of the chain slag scraper, and the box body is filled with water, through which the slag is cooled and sealed. The chain slag scraper is driven by a motor, and the slag is scraped out by the scraper on the lower chain, and then transported to the material pit for storage by the slag conveyor belt. The chain-type slag scraper is driven by a standard metal roller chain, which has strong tensile strength and wear resistance. Scraper brackets are welded on the links, so it is not necessary to use special links for scraper, and the scraper can be freely increased and decreased. The density of slag must be heavier than water, and the scraper can effectively contact with slag.
3 problems existing in the traditional slag discharge method
There are many problems when the chain-type slag scraper is applied to the biomass fixed-bed gasifier. During the operation of the slag scraper, the transmission chain often gets stuck, jumps and breaks, and the two sets of circular chains are unequal in length due to uneven stress, and the scraper and the shell are scratched, stuck and bumped. Mainly manifested in the following aspects:
1) The ash after biomass gasification is mainly charcoal, the density of which is lower than that of water. When water seal is adopted, a large amount of charcoal floats on the upper section of the lower slag bucket for a long time, which leads to a large amount of carbon slag accumulation on the water surface and deformation of the lower slag bucket.
2) During the operation of the slag scraper, the floating charcoal will be scraped at the back when the upper scraper moves backward. Under the squeezing action of the scraper, the charcoal at the back will accumulate densely, which will cause the slag scraper to be stuck. During the operation of the slag scraper, the deviation of the chain will cause less slag to be fished out in a unit time, resulting in that all the slag discharged twice cannot be fished out in a time interval. With the gradual accumulation of carbon slag, the load of the slag scraper is getting bigger and bigger, especially at the end of slag discharge, as the slag in the slag scraper is deposited at the bottom, the resistance to the scraper is gradually increased, which leads to the over-current of the driving motor and the trip. In addition, the slag discharged each time contains some fine slag more or less, which is easy to stick to the scraper and fall off and accumulate on the upper part of the slag catcher, which will increase the load of the slag catcher, increase the current and the force on the chain during the operation of the slag catcher, and lead to the tripping of the slag catcher and the fracture of the chain.
3) With the extension of the operation time of the slag scraper, the main sprocket will gradually wear at the meshing part with the chain, and when the strength of the chain is not enough, the chain will also become longer. When the wear increases to a certain extent, the main