Pernis
The Netherlands - Mechanical vapour recompression
| Summary Propylene is a key material in the production of a number of chemical products including polypropylene (PP) and solvents. It is obtained by distillation separation of propylene and propane in a so called PP-splitter column. In a conventional distillation the reboiler is heated by low pressure steam and the overhead vapours are cooled with cooling water. As a part of the modernisation of the whole propylene distribution system within the Shell site at Pernis, a new propylene-propane distillation column was built with the application of mechanical vapour recompression (MVR), built by Mannesmann Demag AG. This was done to save energy, reduce the use of cooling water and increase the yield of the distillation process. |
Industry/process
| Industry type: | Chemical industry | |||
| Location: | Pernis near Rotterdam, the Netherlands | |||
| Description of the process: In the present new situation the overhead top vapours are used to heat the bottom of the distillation column. The top vapours are compressed in an electrically driven two-stage fixed-speed centrifugal compressor to a higher pressure and therefore a higher temperature. The recompressed overhead vapours are condensed in a condensor/reboiler with UOP Hi-flux double enhanced tubes to heat the bottom stream from the polypropylene (PP)-splitter. The main part of the condensed vapours is returned to the column as reflux, with the remainder providing feedstock to downstream chemical plants. Because the column can operate independently of a cooling fluid, the column pressure can be reduced resulting in a better split between propylene and propane by the increase of relative volatility. The splitter thus produces polymer grade propylene with a purity of min. 99.5 wt% (this used to be 90 wt%). |
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Heat pump system
| Application: | Distillation | |||
| Heat pump type(s): | MVR | |||
| Heat pump installed capacity (kW) | 50 200 | |||
| Drive energy: | Electricity | |||
| Refrigerant: | None | |||
| Heat pump system completion date: | October 1995 | |||
| Description of the heat flows: The overhead vapour from the distillation column is compressed. It then reheats the bottom product and condenses. After further cooling, part is refluxed (see description of process). |
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Performance
| Energy | Heat pump drive energy (kWh/year): | 50 400 MWh/year |
| Fuel: | Electricity |
| Energy output, useful heating (kWh/year): | 401 600 MWh/year |
| Energy output, useful cooling (kWh/year): | 352 000 MWh/year |
| Energy cost (EUR/kWh): | 136 EUR/kW demand charge |
| Coefficient of performance (COP): | 14.9 if heating and cooling are added |
| Test conditions: | No data |
| Heat pump cost breakdown | No data A grant of approximately EUR 2 million was given. |
| Alternative system (if has been considered) | No data |
| Payback | 2 years. At a natural gas price of 0.11 EUR/m3 and an electricity price of 0.05 EUR/kWh an annual energy cost saving of 3.5 million EUR is estimated. At the time of calculation the increase in the production yield of the new process by the higher purity was still uncertain. |
| CO2 emissions | CO2 emissions reduction of 67 kton/year. Electricity is generated at an efficiency of 40% by gas-fired power plants. |
Operational experience and other comments
Maintenance problems have not occurred during the six years of operation. The company has experienced the systems to have a very high reliability.
Next to saving on heating, a considerable saving on cooling energy has been achieved, thus also reducing the use of surface water and disposing of waste heat on surface water.
An increase in the product quality can make this type of energy saving measures popular within industry.
High reliability of the system has been achieved by the advanced process control system developed by Shell (Shell Multivariable Optimization Control).
Contacts
|
Contact 1: |
Onno Kleefkens |
| Company: | SenterNovem |
| Role: | Information |
| Address: | Postbus 8242 3503 RE Utrecht THE NETHERLANDS |
| Telephone: | + 31 30 239 3449 |
| Fax: | + 31 30 239 3703 |
| Email: | O.Kleefkens @ senternovem.nl |
| Last updated: 10 May 2004 |
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