Cel The aim was to implement and evaluate the performance of a novel heating and mixing system at an industrial anaerobic digestion plant. Both heating and mixing units operated in conjunction as part of a combined externally mounted system. External heating and mixing systems are easier to maintain and repair than internally mounted systems, but are generally expensive to operate and can be inefficient. The novel system evaluated here is more efficient than comparable systems and has not been demonstrated before. Successful operation could result in the potential for widescale adoption in the industrial effluent and sewage treatment sectors resulting in significant energy savings. There are two innovatory aspects to this installation. A heating unit which is more efficient than a traditional industrial boiler, and a gas/liquid mixing system based on liquor recirculation and a venturi mixing device. Neither system has been applied to an anaerobic effluent treatment plant before.L%Six steady state periods were selected and evaluated using the monitoring information available for the heating system. Three separate efficiencies were calculated: a Submerged Combustion Unit Efficiency comparing the gross calorific value of the gases used with output to the hot water circuit; a Heat Exchanger Efficiency between the hot water circuit and the digester liquor circuit, and a Overall Efficiency between the calorific value of the gases used and the heat input to the digester as hot liquor. The Submerged Combustion Efficiency averaged 82% but ranged from 68% to 96%. The manufacturer suggests an efficiency of 93% at a tank operating temperature of 50 deg. C rising to 95% at a tank temperature of 35 deg. C. This is a transfer efficiency to the water in the submerged combustion tank. In this installation, additional losses can occur from the tank and through the pipework prior to the heat exchanger. The Heat Exchanger Efficiency averaged 57% and ranged from 52% to 62%. This additional efficiency would also be applicable to a typical boiler system generating hot water. When Heat Exchanger Efficiencies were high, Submerged Combustion Efficiencies were low. There is no obvious reason for this. The Overall Efficiency averaged 47% and ranged from 38% to 51%. The mixing system was evaluated by using a Lithium Chloride Tracer Study. The digester includes two mixing systems should one fail for any reason. The gas spare system incorporates 16 nozzles distributed across the base of the reactor and represents the traditional approach to digester mixing. The venturi mixing system is novel and combined with the heating system in this system. The digester installation is equipped with two compressors on site which can be used to supply the mixing system with biogas, a 15 kW unit and a 22 kW unit. The gas sparge system was evaluated first using the 22 kW compressor. Inert tracer was added to the digester and effluent samples were evaluated over a period lastingup to two weeks, depending on the concentrations recorded. The venturi system was evaluated next, but the 22 kW compressor failed at this point, and it was some time before it could be returned to site. The study concluded that the mixing profile was of the two arrangements was very similar eventhough the venturi system was driven by a compressor with 7 kW less power. Although the venturi was not evaluated with the 22 kW compressor in place, it is anticipated that the mixing profile would be significantly better. The mixing profile with the venturi system was at least as good as the traditional gas sparge system using a smaller compressor. This represents a significant potential saving.The project was technically successful and the system operates reliably and effectively. Apart from the installation of the additional heat exchanger the system performs as anticipated and has fulfilled all technical expectations. The heating and mixing system operated more efficiently than a traditional boiler.This EC contract supports the installation of a combined submerged combustion heating system and a venturi mixing system for an industrial effluent treatment plant at Hall & Woodhouse Limited. The treatment plant comprises a feed pit, digester tank, two dissolved air flotation systems (DAF). The 3300 m3 digester tank is fully clad and insulated, and operates on a variable volume basis. The digester is fitted with two mixing systems, a traditional gas sparge system consisting of 16 equally spaced nozzles situated across the floor of the digester tank and the novel mixing system. Effluent from the digester passes to two DAF units operated in series. Sludge collected in the DAF units is returned to the digester through a weir tank on the roof. The final effluent is discharged from the DAF units, directly to sewer. The heating system comprises a submerged combustion (SC) burner which is fuelled by biogas produced by the anaerobic digestion process, or natural gas as a secondary supply. The gaseous fuel is appropriately carburated before being combusted below liquid level in a combustion chamber, submerged in a water tank. This results in little heat loss since the burner is surrounded by the material being heated, and further heat is recovered from the exhaust gas as it bubbles out of the tank to atmosphere, and partially recondenses. Water from the submerged combustion tank (50-55 deg. C) is recirculated through a heat exchanger by a water pump. The water in the heat exchanger is used to heat the contents of the digester to approximately 35 deg. C. Digester liquor is pumped through the secondary circuit of the heat exchanger by the venturi pump. The digester must be mixed as well as heated to ensure that there is no thermal stratification within the tank, that incoming feed is evenly distributed within the digester and that solids do not accumulate within the tank. This is achieved through the novel application of a venturi mixing system. This comprises two pumps which draw liquor from the digester and pump it back into the digester through a venturi. The venturi mixer is situated immediately outside the digester tank and enables the injection of biogas, delivered from the heat space of the digester, into the narrow throat venturi. One of two biogas compressors are used for this purpose and the gas flow is split evenly to each venturi on opposite sides of the tank. As liquor passes through the venturi throat, the velocity increases resulting in reduced pressure. This enables biogas to enter the stream and form small bubbles before the hot liquor is injected into the tank. The two liquor recirculation pumps are situated on opposite sides of the digester at about 1m above ground level. The outlets point downwards and inwards at an angle to the radius of the tank. This results in a swirling motion, and the bouyant bubbles also rise to provide vertical motion, turning the contents over. Program(-y) ENG-THERMIE 1 - Programme (EEC) for the promotion of energy technology in Europe (THERMIE), 1990-1994 Temat(-y) 2.3 - INDUSTRY Zaproszenie do składania wniosków Data not available System finansowania DEM - Demonstration contracts Koordynator HALL & WOODHOUSE LTD Wkład UE Brak danych Adres THE BREWERY BLANDFORD ST. MARY DT11 9LS DORSET Zjednoczone Królestwo Zobacz na mapie Koszt całkowity Brak danych
