Mechanical Vapor Recompression

Spilling steam compressors are tailor made units, designed for each project individually, based on piston compressors with very good inner efficiencies, resulting in very good COP factors. As it is operated with variable speed, the compressor can operate with flexible steam flow rates between 35 and 100% load.

The steam compressors are typically designed as single stage or double stage compressors (depending on the required pressure ratio – up to factor 2,5…3 typically as single stage unit, above typically as double stage unit).

• Typical intake pressures are between 1 and 20 barg.
• Typical outlet pressures are in the range of 3 to 35 barg.
• Typical pressure ratios P(out)/P(in) (calculated in bar(abs) each) are between factor 1,5 and 5.
•  Typical steam flow rates are between 3 and 20 t/h.
• Power Scale: typically ~ 1,5 to 15 MW(th), corresponding ~ 2 to 20 t/h of steam.
• The power required for the driving the electric motor is comparatively low. For compression pressure ratios (P(out)/P (in)) of factor 1.5 to 5, each kWh of electricity used enables about 5 to 15 times the amount of steam energy to be reused.

• “Steam Recycling” where the (low-pressure) excess steam source and the (high-pressure) steam consumer are independent processes.
• “Closed Steam Cycle” with (typically an overpressure) dryer, where evaporating moisture from the dried product is compressed (after a cleaning stage) to a higher pressure/temperature level and used as heat source for the dryer. Ideally no additional heat input in this process is necessary, it supplies itself with the required amount of high pressure steam.

Model calculation:

In a chemical plant, up to 6 t/h of steam of 4,5 bar(abs) is generated when cooling a distillate. Since there are no customers for this pressure level in operation, the unused steam has been released into the environment via air cooled steam condensers. By compressing excess steam with a steam compressor to 9 bar(abs) and feed it into the company’s internal steam network, the vapor can be re-used, and the natural gas-fired steam boiler can be relieved. With a steam flow rate of 6 t/h (or approximately 4.2 MW(th) heat content in the 9 bar steam) and 6,000 full load hours, 25,200 MWh per year of thermal energy can be provided and the gas consumption in the steam boiler can be reduced accordingly. The electrical power required for compression of nominal 390 kW(el) amounts to 2,340 MWh per year, which corresponds to approximately 9,5% of the reusable steam output. If the additional demand for electricity and the natural gas savings are multiplied by the corresponding emission factors and countermeasures result in a CO2 saving by the implementation of measures of approx. 3,900 t per year. Costs for implementation: Investment costs for steam compressor (incl. engineering and commissioning) €700,000, additional investment costs (for pipes, electrical works, building, overall engineering, external connections to electricity and steam) in the amount of approximately € 500,000 -> total investment costs of approximately € 1,200,000.

• Lower fossil fuel consumption (and maybe also avoidance of cooling capacities /expenses to condense excess steam)

• Globalfoundries (former AMD), Germany
• Vattenfall, Germany
• CAPCO, Taiwan
• APU, Mongolia
• and others

Spilling Reference Sheet Steam Compressors for Steam Recycling