The application of briquetting in various chemical, mineral, mining and metallurgical processes has been rapidly increasing in the past two decades. This is, in part, due to the development of new, more economical and higher performance briquetting equipment. Some of these developments, which have reduced the operating and maintenance costs, include anti-friction bearings, hydraulically applied pressure enclosed and sealed gearing and bearings, tapered predensification feed screws, water cooling and materials of construction capable of operating at temperatures up to 1800°F, and control systems capable of maintaining optimum briquette quality control.
The briquets can be formed into almost any desired size and shape. To date, with present rotary briquetting presses in the 25 to 500 ton force range, briquets from ¼” to 6″ length are presently being used. The screw force feeder, which can be of various taper configurations or straight, performs several other functions in addition to feeding the material to the press rolls. Of equal and possibly greater importance, they (1) predensify or precompact the material, prior to its entry into the roll forming dies, (2) apply a precompaction pressure to the feed material and (3) deaerate the feed material by means of the precompaction pressure. These functions have a major effect in producing a satisfactory briquet.
Increasing the precompaction pressure p from a gravity value of 0.1 PSI to a force fed screw value of 10 PSI, theoretically decreases the roll diameter by 50%. At 50,000 PSI briquetting pressure, the theoretically indicated roll diameter at 0.1 PSI precompaction pressure is 42″, and at 10 PSI, the roll diameter is 19″.
Change in bulk density of the feed material is one of the most common variations in the process feeding system that can affect the briquet quality. An increase in precompaction pressure at constant roll drive speed increases the production rate, the briquet density and the roll drive horsepower.
Variable speed feeder drive control systems which can maintain, constant screw torque and precompaction pressure are obtainable in various hydraulic, mechanical and electric control arrangements. A frequently used present day arrangement, developed and patented by K-G Industries. Variations in precompaction pressure, and the corresponding roll briquetting pressure, are sensed by means of directly related variations in the roll drive motor amperage. The optimum precompaction pressure and corresponding briquet press design configurations vary widely with the many physical and chemical properties of the material and also with the desired quality and shape of the briquet.