Over the years Thermax has developed many fabric filtration systems, thereby achieving a number of significant breakthroughs and industrial application milestones on the way. On the Reverse Air Bag House front, these include the first installations for carbon black, cement kiln and sponge iron de-dusting applications built in India.
Other major applications handled, were for ferro-alloys and other metallurgical processes and lime kilns. These systems have been designed to clean emissions from various industrial processes and handle a wide range of gas volumes – from 60,000 m3/hr to more than 10,80,000 m3/hr. Depending upon the duct characteristics, Thermax offers the most economical and efficient cleaning method to minimise pressure drop across the bag house.
The Reverse Air Bag House (RABH) is a custom-built filter, designed for cleaning gases with typically high flow rates and high temperatures.
The typical Thermax RABH is modular in construction, with four or more independent modules – the modules being set in pairs, when the gas flows are on the higher side. The sealed air gap between the modules, adds to the insulation to increase operating economy. The extra space created by the hoppers provides a large passageway between rows down the middle of the system. This passageway is divided into three sections horizontally to make the inlet plenum, outlet plenum, and the reverse-air plenum.
This construction and operation of the units not only offers control on velocity profiles, but also facilitates on-line maintenance. Each module can be isolated for inspection or maintenance by closing the inlet, outlet and reverse air damper, while other modules are in operation. The units – being custom built and voluminous – are despatched knocked down to structurals and panels.
Normal Gas Flow
The dirty gas to be cleaned enters the common inlet air plenum. A portion passes through each inlet air damper into the hopper area below each module. The dust laden gas passes through the tube sheet to the inside of each bag. Virtually all the gas bored particles are separated as the gas passes through the bags to meet performance levels. Clean gas enters the outlet plenum through the open outlet damper and moves out through the clean gas outlet.
Reverse Gas Flow
Each module is periodically and automatically shut-down for a brief reverse-air cleaning as per the system logic. Clean hot gas is drawn from the outlet plenum by the reverse-air fan into the reverse-air plenum during cleaning. During the process, the outlet damper is closed and the reverse-air damper is opened, letting in the reverse air in the opposite direction from the normal dusty gas flows. This action slowly collapses the bags breaking up the dust cake on the inner bag surfaces allowing the dust to get discharged to the hopper.