Review of briquette binders and briquetting mechanism

Briquette binder plays a key role in the process of briquette production. The quality and performance of briquette also depend on the quality of briquette binder. Different types of briquette need different briquette binder. Binder used in briquetting process can be divided into inorganic binder, organic binder and compound binder. The inorganic binders have many excellent advantages, such as abundant resource, low cost, excellent thermos-ability and good hydrophilicity. However, a major problem arising from the usage of inorganic binder is related to the ash increased in significant amount. The organic binders have many excellent advantages, such as good bonding, good combustion performance and low ash. But organic binder is easy to decompose and burn when it was heated, so the mechanical strength and thermal stability of organic binder briquette are poor, and its price is high. The composite binders are composed of two binders at least; the different binder plays the different role. The compound binder can make full use of the advantages of all kinds of binder, such as it can reduce the supplying amount of inorganic binder, reduce the cost of organic binder, improve the quality of briquettes, and get better performance of briquettes. This review will cover briquette binder literature. Due to many factors taking into consideration for briquettes process, up to the present, no uniform mechanism has been developed to solve briquette production. The clarification of briquetting mechanism of briquette binder is not only can provide a theoretical basis for binder development, but also can provide instructive theory for briquette industrial production. There are five main theories of non-binder briquetting mechanisms: bituminous hypothesis, humic acid hypothesis, capillary hypothesis, colloid hypothesis and adhesion molecules hypothesis respectively. But those hypotheses cannot fully explain the briquetting issues about lignite. There are three main theories binder briquetting mechanisms from the view of interaction of binders and the pulverized coal: solid bridge connecting, electrostatic attraction and liquid bridge connecting respectively. In this paper, the process of non-binder briquetting mechanism and briquetting mechanism with binder is also reviewed.