Chemical Reaction

A b o k at modulur,j2ek€-erected mass-burn, and RDF systems, as well as a peek at two e m q i n g &xlmologies, provides an overuim of &e options for tkrtnul reduction of refue volume. T wo methods of producmg energy from waste have emerged as most preferred by communities and industries: the " mass burn " system, in which unprocessed waste is incinera-ted and energy recovered; and the " refuse-derived fuel " (RDF) system, in whch unprocessed waste is processed into a usable fuel. RDF is burned in either a dedicated boiler or as a supplemental fuel in a coal-fired boiler. State-of-the-art mass-burn or RDF facilities do not require that waste be source-separated or prepro-cessed, other than removlng large non-burnable objects (i.e., ergme blocks and refngerators). These system, and their variations, are described in this lesson. Adequate furnace temperature is fundamental to good Combustion. Heat is the dnmg force which sustains the combustion process. At low furnace temperatures, incomplete combustion may result in air pollutmg emissions. As furnace temperature rises, more complete breal-down of combustion products occurs. Supplemental heat is often supplied by an auxiliary burner to support the combustion of wastes with hgh moisture content andor low heat value, or to pre-heat the incinerator. ''Time " refers to the residence time of air and gases within the incinerator. Too short a residence time wdl result in poor combustion. Residence time is computed by: chamber volume (cu.ft) = time (set,) gas flow (cu.ft/sec.) Example for a primary chamber: 5,000 cubic feet divided by 10,640 cubic feet per second = 0.47 seconds. Residence time is estabhshed by desigrung combustion chamber volume relative to the rate at which gas will flow through the incinerator. The volume must be large enough to retain the gas flow long enough for complete combustion of the solid waste and volatile gases. ducts of combustion with air. Turbulence is enhanced by baffles constructed inside the incinerator plus the strategic placement of ducts within the incinerator. Changes in du-ection plus gas velocity increases due to constrictions, detennine the extent of turbulence as the gases move through the system If turbulence is not sufEcient, separation or stratifica-tion of the combustion gases w i l l occur. With insufficient turbulence some of the gases will go through the incinerator unburned. Since solid waste is not a uniform m a t e d , this is an important consideration. …