Vapor-compression evaporation

Very large units (evaporation capacity 100 metric tons per hour or more) sometimes use Axial-flow compressors.

For this reason, the vast majority of MVR units feature a desuperheater between the compressor and the main heat exchanger.

The efficiency and feasibility of this process depends on the efficiency of the compressing device (e.g., blower, compressor or steam ejector) and the heat transfer coefficient attained in the heat exchanger contacting the condensing vapor and the boiling "mother" solution/liquid.

The evaporation process may be solely driven by the mechanical work provided by the compressing device.

While this cannot compete in the marketplace with reverse osmosis or demineralization, vapor compression chiefly differs from these thanks to its ability to make clean water from saturated or even crystallizing brines with total dissolved solids (TDS) up to 650 g/L.

Since boiling point elevation determines the pressure ratio in the compressor, it is the main overall factor in operating costs.

The technology used today to extract bitumen from the Athabasca oil sands is the water-intensive steam-assisted gravity drainage (SAGD) method.

[1] In the late 1990s former nuclear engineer Bill Heins of General Electric Company's RCC Thermal Products conceived an evaporator technology called falling film or mechanical vapor compression evaporation.

In 1999 and 2002 Petro-Canada's MacKay River facility was the first to install 1999 and 2002 GE SAGD zero-liquid discharge (ZLD) systems using a combination of the new evaporative technology and crystallizer system in which all the water was recycled and only solids were discharged off site.

[1] This new evaporative technology began to replace older water treatment techniques employed by SAGD facilities which involved the use of warm lime softening to remove silica and magnesium and weak acid cation ion exchange used to remove calcium.

The evaporators, when coupled with standard drum boilers, produce steam which is more "reliable, less costly to operate, and less water-intensive."

By 2008 about 85 per cent of SAGD facilities in the Alberta oil sands had adopted evaporative technology.