beedes – thermal process engineers Compact Heat Exchangers in Industrial Evaporators Fred Brotherton
beedes – thermal process engineers Introduction A recent study has shown that in the UK the Food and Drink sector may account for up to 15% of the total energy used in the Process Industries. Over 60 % of this relates to low temperature processes, with distillation, drying and evaporation making significant contributions. Conservative estimates suggest that a reduction of at least 10% is possible using existing heat recovery techniques, and compact plate heat exchangers have a part to play in achieving this. This presentation will describe some novel ways in which the particular characteristics of gasketted plate heat exchangers have been used to improve process efficiencies.
beedes – thermal process engineers Plate Heat Exchangers
beedes – thermal process engineers Plate Heat Exchangers Gasketted plate heat exchangers are available in a wide variety of corrosion resistant materials including stainless steel. The angle of the chevron corrugations on the plates is varied in order to change the relationship between heat transfer and pressure drop. The contact points between adjacent plates contributes to the mechanical strength of the assembled plate pack.
beedes – thermal process engineers Plate Heat Exchangers
beedes – thermal process engineers Plate Heat Exchangers The plates are assembled in a support frame to provide alternate passages for the two or more fluids which are exchanging heat. Tie bars are used to clamp the plates in position. Two or more passes can be provided in order to give the required thermal performance. The flow in most of the passages is counter-current.
beedes – thermal process engineers Plate Heat Exchangers
beedes – thermal process engineers Freeflow Plates
beedes – thermal process engineers Freeflow Plates The plates are designed to provide flow channels that are free from contact points. The flow channels are separated by additional rubber gaskets or corrugations on the plates.
beedes – thermal process engineers Freeflow Plates
beedes – thermal process engineers Effluent Evaporator (before)
beedes – thermal process engineers Problems with Original Design Hot water flowpath is complicated. High product recirculation rates are required. Low pressure in condenser is required.
beedes – thermal process engineers Effluent Evaporator (after)
beedes – thermal process engineers Benefits of New Design Hot water flowpath is simplified. Product recirculation rates are reduced. Pressure in condenser is higher. Temperature profiles for hot water and product are optimised, and hence thermal efficiency is improved. Pumping power for hot water, product and cooling water is reduced.
beedes – thermal process engineers Further Developments Calculations showed that additional benefits could be realised by combining the use of plate heat exchangers heated by hot water and falling film evaporation in a hybrid system. These concepts are now being used to modify an existing evaporator.
beedes – thermal process engineers Another Effluent Evaporator (before)
beedes – thermal process engineers Problems with Original Design Hot water flash in one stage severely constrains design. Large surface area required in each effect. Low pressure in condenser is required.
beedes – thermal process engineers Another Effluent Evaporator (after)
beedes – thermal process engineers Benefits of New Design Pressure in condenser is higher. Temperature profiles for hot water and product are optimised, and hence thermal efficiency is improved. Pumping power for hot water, product and cooling water is reduced.
beedes – thermal process engineers What Next? The exhaust from a dryer can have a significant latent heat content, but this can only be recovered at low temperatures. Evaporators have been designed to be heated by the exhaust from a dryer directly, but the design must accommodate the non-condensible gas flow. Gas scrubbers using impingement plates can be designed to recover hot water at temperatures suitable for use in existing designs.