Heat recovery through retrofitting
Vapor recompression has energy savings potential
For many applications, the evaporation technology as a traditional thermal separation technology is still unrivalled. Those wishing to cut operating costs should consider the possibility of a system retrofit through vapor recompression. In GIG Karasek’s opinion, this technology is best suited to meet the industry‘s current needs in terms of availability and energy efficiency.
Let us assume a wheat starch production facility producing 40 tons of wastewater per hour which are fed into an evaporation plant. The evaporation rate is about 35 tons/h. For a six-effect evaporation plant, the steam consumption is 6.3 tons/h. Assuming that the cost of vapor generation is 30 euros per ton , the total energy cost is as much as 189 euros/h. When retrofitting a mechanical vapor recompression, main steam is only used for starting up the system and to compensate the energy balance. This means that the system is run almost exclusively with electricity.
Using a mechanical vapor recompression, in this case power consumption tipically amounts to some 700 kWh. Assuming a power cost of 0.1 euros/kWh the total cost is 70 euros/h. Thus, by implementing a mechanical vapor recompression system the operating costs of the evaporation plant decrease by 129 euros/h.