Study On Preparation Of Pressurized Gasification Briquette From Low-rank Bituminous Coal

Coal gasification is a clean and efficient way to use coal.Using pulverized coal under pressure as raw material of Lurgi gasifier can not only solve the problem of insufficient supply of block coal,but also make full use of pulverized coal.Low rank coal has good chemical activity and easy gasification.It is of great significance to establish a clean energy system for sustainable development by molding low rank coal for gasification.In this paper,long flame coal is used as raw material,for the purpose of develop coal binder for gasification briquette,based on the action principle of binder and the requirements of Lurgi gasifier for briquette,the basic formula is developed.From two aspects of improving the thermal strength and the hot water resistance of the briquette,a kind of compound binder formula with excellent performance was obtained.The properties of briquette were improved by optimizing briquette forming technology,and the mechanism of briquette was studied.The main conclusions are as follows:(1)According to the bonding mechanism of binder and the requirements of gasified briquette,three kinds of binders,pre-gelatinized starch,bentonite and tar pitch,are selected as the basic formula.Through analysis,the effect of starch on the cold strength of briquette is significant.Bentonite has a significant influence on the thermal strength and thermal stability of briquette.The addition of starch is 2%,the amount of bentonite addition is 7%,coal tar is added.Under the condition of 5%,the performance of briquette is the best.(2)The influence of molding pressure,particle size distribution,molding moisture and bonding agent on the strength of briquette was studied.Finally,the optimum molding pressure was determined to be 20 MPa,Finally,the optimum molding pressure is 20 MPa,the optimum amount of water added to the molding is 10%,the size of coal particle size <0.15 mm accounts for 40%,0.15 ~ 0.5mm accounted for 25%,0.5~2mm accounted for 25%,2~3mm accounted for 10%.(3)Combined with the bonding mechanism of briquette and the apparent structure analysis of carbonization process,the carbonization process of briquette can be divided into three stages:the first stage is the solid and solid stage,the coal powder is tightly surrounded by the binder,and the briquette has higher strength.The second stage is solid adsorption.With the increase of temperature,the pregelatinized starch and coal tar pitch begin to soften and become colloidal,and the strength of briquette decreases.the third stage is the solid and solid stage,The residue of coal tar pitch decomposition and bentonite act as binders at high temperature.With the increase of temperature,water evaporates and concentrates,The adhesion state of binder on coal surface changes gradually,starch has been decomposed at 450 ℃,the particles of binder on the surface of coal begin to decrease,begin to depolymerize and decompose reaction,produce gas and appear a little pore structure.When the temperature reaches 650 ℃,a large amount of volatile precipitates separate out lead to a lot of holes on the surface.In the later stage of carbonization,(450~650 ℃),the type of coal is solidified and contracted,and some of the gel permeates the pores.When the carbonization temperature reaches 850 ℃,the pore structure is more,the coal surface is mainly flake montmorillonite,and the binder exists in the form of bridge.(4)Through the high temperature steam scouring experiment,it is found that the briquette with better waterproof is less reduced by the steam scouring strength.After a lot of tests,it is found that a water-repellent agent,aluminum dihydrogen phosphate,can significantly improve the thermal waterproofing of briquette.The 360 min water absorption rate of the briquette is 31.7% when the type coal is carbonized without water repellent mineral salt.When mineral salt is added and after carbonization at 850℃,the water absorption of 360 min is 7.5%,Water absorption reduced by 24.2 percentage points.