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Show GASEOUS AND LIQUID WASTE FUEL CASE STUDY Gas Atomized Pyrolysis Fuel Oil in a Boiler: In this application, the production capacity of a petrochemical ethylene plant has been expanded and new boilers are being added. These new boilers are designed to fire the continuous production of waste gases and liquids from the ethylene process. The project is funded by the World Bank and strict N O x and particulate emissions requirements are being enforced. The project will utilize gas atomization of the waste liquid to allow for an efficient design and for N O x and particulate emissions performance. Gaseous fuel: Ethylene unit off-gas is a gaseous stream of varying composition leftover from the ethylene production process. The stream is predominately made up of methane with varying amounts of hydrogen and propane depending upon the Ethylene unit feedstock. This gas is collected in a mix drum and the mix is fired in the boilers. Liquid Pyrolysis Fuel Oil (PFO): The liquid PFO is a blended combination of pyrolysis side cut, pyrolysis bottom cut, and C 9 plus product and is recovered as a byproduct of the hot fractionation section from an ethylene unit. This liquid is the residue from severe thermal processing and has a tendency to polymerize at high temperatures making steam atomization problematic due to atomizer fouling. The P F O has similar viscosity characteristics to a No.4 Fuel Oil and a carbon residue similar to a No.6 Residual Fuel Oil. The pentane insolubles in the P F O indicates a high content of asphaltenes and the Conradson Carbon indicates a high potential for coke formation leading to increased particulate emissions and potential carbon build up on the burner tip. During normal operation, 3 0 % of the boiler load will be fired with liquid byproduct waste, and 7 0 % of the boiler load will be fired with the off-gas. There is a potential for the heat input from the P F O to reach a m a x i m u m of 5 0 % of the boiler load, not including the heat input required from the atomizing off-gas. Tangentially fired Combustion Engineering VU-60 boilers (furnished by Cerrey) are selected for the service, see Figure 1. With the tangentially fired furnace the fuel and air are projected from the corner wind boxes along a line tangent to a small circle. A large-scale, rotational motion similar to a cyclone is created in the center and the burning process occurs in the furnace volume in the form of a "fireball." To achieve m a x i m u m flexibility, the boilers are equipped with four burners located to fire in a tangential arrangement. Each of the four Figure 1: Tangentially Fired Boiler (from Combustion: Fossil Power, 1991) 3 |