BAGHOUSE SYSTEM DETAIL

A Dry Scrubber System is comprised of three (3) primary components:

• A Gas Cooling System
• A Reagent Injection System
• A Fabric Filter (Baghouse) System

In addition, there are several subsystems that all must be properly integrated to provide a working system.

Click each feature's title to see the system schematic.

Inlet Breeching:
The hot gas (usually 1800° F+) is ducted to the gas cooler in refractory lined breeching. Support and thermal expansion are the major design challenges. Often an emergency dump stack is included.

Gas Cooling:
The flue gas must be cooled to enhance the removal of acid gases and toxics, and to be compatible with the materials of construction. Control of condensation and corrosion is critical.

Reagent Injection System:
The reagent system is comprised of Material Selection, Reagent Storage, Injection Method, and in the case of dry injection, Reagent Feed. Each of these issues has design alternatives that need to be considered on a case specific basis.

Material Selection:
Although there are other alternatives available, most often the decision is between lime based reagents (usually hydrated lime) and sodium based reagents (sodium bicarbonate and naturally occurring sodium carbonate/sodium bicarbonate minerals).

Reagent Storage:
The reagent storage method is almost always determined by the usage rate. For the smallest systems day bins are used with reagents that are packaged in 50 lb. bags, and generally delivered by pallet loads. Intermediate systems use a bulk bag system with typically 1 ton bags, and an integral crane system for bag handling. In larger systems, bulk storage silos are used. These can accept full truck or even rail car deliveries.

Injection Method:
The acid gas scrubbing reagent is either mixed into a slurry which is atomized into fine droplets and sprayed into a spray dryer (semi-dry scrubbing); or the reagent is injected as a dry, fine powder into the cooled gas (dry scrubbing). A specially designed venturi provides thorough mixing of the reagent and acid contaminated gas stream.

Reagent Feed:
In the case of dry reagent injection, the material can be conveyed either by gravity or pneumatic conveying for injection. In come cases, mechanical conveying can be used, but then the actual injection is still basically by gravity.

Activated Carbon System:
A dry activated carbon powder can be injected to adsorb dioxins, furans, Mercury, and other toxins. This injection takes place after the gas cooling and may be done in a blend with a reagent for acid gas scrubbing. The carbon can be stored and fed in the same manner as the reagent.

Baghouse and Reaction Vessel:
The reacted acid gases and adsorbed toxins are removed in the baghouse. In addition to the reaction that has taken place in the gas stream prior to the baghouse, the unreacted reagent becomes a part of the filter cake in the baghouse where it provides a considerable amount of additional gas scrubbing. Contact between the flue gas and reagent is particularly intimate because of the dense cake and very slow gas movement. Unlike most competitive baghouses, the BET unit is designed specifically to be a part of an acid gas reaction program. There are unique features in the inlet design, bag spacing, and cleaning mechanism that optimizes the reaction process. See also Baghouse System Detail for more design details and component description.

ID Fan and Draft Control:
An ID fan system provides fast response to a control signal to maintain the draft at the source, regardless of fluctuations in the process. The draft can be controlled either by using a variable speed drive or a modulating damper valve with an automatic operator.