The Gas Heated Evaporator

IN ZERO LIQUID DISCHARGE/EVAPORATIVE WASTEWATER TREATMENT

What is a Gas Heated Evaporator (GHE) and why should it be considered as an alternative to conventional steam and MVR evaporators? A Gas Heated Evaporator is one that taps the energy contained in off-gases from existing plant operations instead of using steam. This can cut evaporator operating cost to near zero or allow added evaporative capacity without increasing energy costs. Proven for more than a decade in corn wet milling and alcohol processing, GHE holds high potential but is still largely overlooked in some areas of chemical, pulp/paper and petrochemical production. These operations tend to produce the type of waste gas streams that are appropriate for the moderate boiling points typical of these evaporative processes. GHE also may prove cost effective in other industries where the cost of steam is high, or where boilers are at capacity.

While the concept of using waste heat is already cutting energy costs in a number of industrial applications, extending this technique to evaporative processing involves specialised design requirements. Dedert has the patent for the heat rating and mechanical design construction of GHE which allows successful continuous operation without encountering fouling and scaling problems on the gas side off the surface areas.
Typical resources are various cooking/boiling/distilling operations, and some dryers, ovens, kilns or incinerators.
Euchem introduced the GHE technology in South Africa with great success six years ago. We have two effluent evaporators and one effluent crystalliser / crystallizer built and commissioned in South Africa working exceptionally well
Page 10 ENERGY INTEGRATION EFFLUENT TREATMENT PLANTS
1200TPD ComodityStream CondensateA CondensateB CondensateC CondensateD CondensateE Gas InletGi Gas OutletGo
Our most remarkable example of effluent evaporation and energy conservation in South Africa is shown in the flow diagram below:

This system is called Energy Integration Effluent Treatment Plant and it is the first of its kind in the world. The plant consists of one effluent evaporator (CSL evaporator) and one effluent salts crystalliser / crystallizer. The effluent evaporator is a triple effect vacuum evaporator for 32.8 tph evaporation capacity. The effluent salts crystalliser / crystallizer is a double effect, forced circulation vacuum crystalliser / crystallizer  for 9.4 tph evaporation capacity. The waste gas stream Gi is utilised to drive both units. In summary, a total of 42.2 tons/h of water is evaporated and recovered as quality process condensate with zero energy input. The only energy consumption is for the pumps and for the vacuum system.



ENERGY INTEGRATION EFFLUENT TREATMENT PLANTS