Vlissingen
The Netherlands - Mechanical vapour recompression
| Summary Since 1982 three steam recompression systems have been in operation at the Hoechst production plant in Vlissingen. The heat pumps are a part of the process for the production of dimethyl-terephthalate (DMT). With the application of steam recompression, steam pressure is increased from 1.14 bara to 3 bara, which can be used in the low pressure steam system. The main goals for the application have been cost reduction and the possibility to work with a smaller steam production plant. |
Industry/process
| Industry type: | Chemical industry | |||
| Location: | Hoechst plant, Vlissingen, the Netherlands | |||
| Description of the process: In the production of dimethyl-terephthalate (DMT) the first step is the oxidation of para-xylene C6H4(CH3)2 with air. The second step is the esterification of the oxidation product (paratoluic acid) with methanol, towards para-toluic acid, methyl ester. This intermediate is oxidised and esterified once again to the resulting DMT (second and third steps). To produce a product with a purity of 99.96%, the DMT is partly purified by distillation. The remaining impurities are removed by crystallisation. In the condenser of the methanol distillation column, steam is generated at 1.14 bara by condensation of the methanol reflux (15 tons/h, 106ºC, 4.2 bar). The generated steam is compressed to 3 bar in a two-stage centrifugal compressor (Linde GT040T2K1, 760 kWe) and supplied to the low pressure steam system. Interstage cooling between the two stages takes place and additional condensate is injected after the second stage of the compressor. A total of 7 tons/h of steam is delivered to the 3 bar steam system. The two-stage compressor is directly driven by a radial centripetal expansion turbine (Atlas Copco, ET410NS). Exhaust gases (19,000 Nm3/h) from the oxidation section of the DMT reactor (mainly N2 and CO2) are expanded from 5.5 bara to 1.25 bara. The outlet temperature is controlled by a by-pass over the expander. Besides this steam compression system, another system is in operation. Steam generated in two oxidators (4.2 and 3.9 bara) is compressed to 5 bara in two electric-driven centrifugal compressors (Atlas Copco GT026T1K, 131kWe and 132kWe). A total of 20 tons/h of steam is produced at 5 bara (=163ºC), which is delivered to the steam grid. |
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Heat pump system
| Application: | Distillation | |||
| Heat pump type(s): | Mechanical vapour recompression (MVR) | |||
| Heat pump installed capacity (kW) | No data | |||
| Drive energy: | Steam/Electricity | |||
| Refrigerant: | Steam | |||
| Heat pump system completion date: | 1982 | |||
| Description of the heat flows: | See above. | |||
Performance
| Energy | Heat pump drive energy (kWh/year): | No data |
| Fuel: | Electricity |
| Energy output, useful heating (kWh/year): | 7 tons/h steam at 3 bara 20 tons/h steam at 5 bara |
| Energy output, useful cooling (kWh/year): | No data |
| Energy cost: | No data |
| Coefficient of performance (COP): | No data |
| Test conditions: | No data |
| Heat pump cost breakdown | No data |
| Alternative system (if has been considered) | No data |
| Payback | 1 year 3 months. This is calculated roughly from the following: Steam driven system: investments EUR 295 000 with cost savings of approximately EUR 270 000 per year. The second system (two compressors): investment EUR 155 000 with cost savings of EUR 725 000 per year. These systems were newly built, so the investment costs are calculated on extra costs compared with traditional systems in a new plant. |
| CO2 emissions | CO2 emissions reductions are 5.3 and 14.2 kton/year. These figures are calculated at assumed efficiencies for the steam boiler of 90% and gas fuelled power generation of 52% and at a running time of 8 000 hours. Energy savings are for the steam driven heat pump calculated at 3 million m3/year of gas equivalent and for the two electric driven systems at 8 million m3/year. |
Operational experience and other comments
The systems are considered as very reliable. Although heat pumps in general are seen as difficult and not very reliable, the heat pumps at Hoechst were not really recognised as such because maintenance costs are extremely low. There have been no operational problems.
Extremely short payback times can be achieved by installing heat pumps at new-built plants from the beginning.
Heat pumps should in the case of MVR systems be marketed as compressors, integrated in systems.
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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