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Sludge thermal treatment - High temperature fluidized bed
International Symposium SIDISA 2012AIR AND SOLID LOW POLLUTION EMISSION IN A SPECIFIC BIOLOGICALSLUDGE THERMAL TREATMENT PLANT– HIGH TEMPERATUREFLUIDIZED BED LE HAVRE CASE STUDYPEDRAZZI Luca*§; DANGTRAN Ky**; LEBONNOIS Damien** Degremont Italia S.p.A.; 57 B. Crespi – Milan, 20159 - Italy.** Infilco Degremont Inc.; 8007 Discovery Drive –Richmond, 23229, VA - USA§ corresponding author e-mail: email@example.comKey words: sludge fluid bed incineration, flue gas analysis, energy recoveryAbstractLe Havre is a port city in Northwestern of France, located on the right bank of the mouth of theriver Seine on the English Channel. In 2011 a new wastewater treatment plant was built and put inservice to serve a population of 415, 000 inhabitants. The sludge treatment is mainly by dewateringwith filter press followed by fluid bed incinerator Thermylis™. Le Havre incineration systemconsists of a high temperature fluidized bed equipped with a two-stage thermal energy recovery,with air preheating to maintain autogenous combustion and hot water production for building heat.Combustion gas is treated by a two-stage air pollution control system equipped with cyclonefollowed by chemical injection and bag-filter.Fluidized bed incineration has been gaining more acceptance over the last few years asmunicipalities focus on green and sustainable technology with maximum energy recovery, andminimisation of the WWTP waste evacuation. One of the major barrier to incineration is theNIMBY (not in my backyard) syndrome. With Le Havre fluid bed system in full operation sinceJune 2011, flue gas pollutants, ash and spent chemicals analysis is presented in this paper, with theultimate goal of providing a case study of emissions for most important air pollutants from sludgefluidized bed incineration plant. This paper will be a useful tool for a novel approach to socialevaluations of the new installation. Energy consumption figures recorded at the plant in comparisonwith drying plant are also presented in this paper.Le Havre incineration plant was designed to treat 1.2 tons of dry matter per hour, or 3.75 tons ofwet cake per hour at 32% dryness and 55% of volatile matter. At design condition, the system shallnot use any fossil fuel and shall produce 0.442 t/h of ash and 0.165 t/h of spent chemicals Chemicalconsumption was designed for 68 kg/h of sodium bicarbonate and 3 kg/h of activated carbon, inorder to respect European environmental limits. The guarantee on the electrical consumption was362 kW el / h.During the first four months of operation, the design capacity of 1.2 ton per day was met and keptconstant even with a sludge dryness of only 25%, much lower than design condition (32%). With anash production close to design, chemical consumption and the by-product spent chemicals waslower than design. Emissions of all gas pollutants including TOC, NOx, SO2, dust, dioxins andfurans are lower than the daily admissible limits (by at least 2 to 10 times). Combustion is completewith an unburned carbon in the ash of less than 0.01%. Heavy metal concentrations in the ash andspent chemicals are close to the detection limits. For the first four months of operation, with a cakePedrazzi, Dangtran and Lebonnois - October 2011 Page1/2
International Symposium SIDISA 2012dryness of only 25% (design = 32%), fossil fuel usage was 700 kWh/ dry ton or five times thedesign value (143 kWh/dry ton), even though much lower than the estimated fuel consumption atdrying plant (3000 kWh/dry ton).During the last month of commissioning, with the optimization of the sludge dewatering equipment,a much dryer cake was obtained (30%), natural gas consumption was reduced to lower than 50kWh/dry ton. Ash from Le Havre plant passes all leachability tests for heavy metals, and can bereused, while spent chemicals are treated for salts recovery.The successful operation at the Le Havre WWTP has shown the modern fluid bed incinerationsystem to be an economical, environmentally acceptable sludge disposal method satisfactory to theAuthority, the permitting agencies and the general public.Pedrazzi, Dangtran and Lebonnois - October 2011 Page2/2