SCHACK LOW BTU COMBUSTORS AND EMISSIONS

摘要

Low btu gas is formed from the incomplete combustion of hydrocarbons. Common processes that produce lowrnbtu gases are petrochemical, blast furnace and carbon black. The combustion process is halted or frozen by coolingrnthe reaction quickly or not supplying sufficient oxygen to the process. The resultant effluent gases are sometimesrncalled process gas or tail gas because the gas is collected at the tail end of the process. These gases can range fromrnabout 60°F to as high as 1200oF ( 15℃ - 650 ℃ ). The lower heating value of this low btu gas is approx. 50 -100rnBtu/scf (466 - 933 kcal/Nm3). The effluent combustible components are CO, H_2, CH_4 and some heavier hydrocarbons.rnIt also contains inert components like N_2, CO_2 and H_2O (mostly from the quench water). Depending on therndegree quench the H_2O content of the low btu gas could be in the range of 30% to 40% on a wet basis.rnWhile in the United States of America most plants were originally designed to vent unburnt low btu gas directlyrninto the atmosphere, in Europe and Asia, where energy always has been at a premium, the energy from the combustionrnof these low btu gas for steam generation has been applied for quite a long time.rnA heat recovery system arranged downstream of combustion plants is mandatory in many countries in Europernbecause it is not allowed to vent the incinerated gas directly into the atmosphere. In the United States of Americarnthe low btu gas has been released unburnt for years. New laws and regulations have forced many producers to addrnincinerators. Since electricity is cheap and incinerator outlet temperatures are limited to as low as 1000°F in somernstates, quenching systems are being used instead of heat recovery systems. Schack has developed a water sprayrnquench lance that is water cooled and removed while in operation. A system of twelve (12) lances that has a maximumrnwater spray of 600 gpm with a 5 to 1 turndown to maintain a 1000°F outlet temperature plus or minus 50°F.rnSteam generation for turbine driven air blowers is also being contemplated in some U.S. plants.rnDue to the large amount of inerts in this flue gases like water vapor and nitrogen, the heating value of the gasrnis very low compared to conventional fuels like oil and natural gas. This results in adiabatic combustion temperaturesrnof only 1800°F to 2000°F (1000℃ to 1100℃) whereas those of oil and natural gas are about 3600°Frn(2000℃). This makes clear that the combustion systems have to differ from those used in conventional boilers.rnRefractory lined combustors, preheated combustion air and support fuel are sometimes required to maintain stablerntemperature.