Haddington
United Kingdom - Mechanical vapour recompression
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Summary This is an example of a single-effect falling film tubular evaporator with mechanical vapour recompression (MVR). The evaporator was installed to increase evaporation capacity on this site due to expansion in production, and it is used to concentrate a range of food products. MVR was chosen in order to reduce operating costs and to avoid the need to install an additional steam boiler. This system achieves a COP of 38 at design operating conditions and significant savings in comparison to a conventional steam boiler. |
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Industry/process
| Industry type: | Food | |||
| Location: | Haddington, East Lothian, UK | |||
| Description of the process: Pure Malt Products Ltd produce a wide range of malt extracts at their Haddington factory near Edinburgh. These find many applications in the food and beverage industries, which demand the highest standards of production. Evaporation is a key operation in the manufacturing process. Pure Malt Products Ltd use single- and multiple effect evaporators designed to provide the optimum processing conditions for each product. Until recently, all the evaporators were heated by steam, representing the major use of steam on site. |
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Heat pump system
| Application: | Evaporation, in the food industry | |||
| Heat pump type(s): | Mechanical vapour recompression | |||
| Heat pump installed capacity (kW) | 75 | |||
| Drive energy: | Electricity | |||
| Refrigerant: | No data | |||
| Heat pump system completion date: | January 1999 | |||
Description of the heat flows:
Vapour from the evaporator is compressed in a centrifugal compressor. This vapour is returned to the evaporator where it condenses acting as the main heating medium for the process. Evaporation is carried out in three falling film stages combined in one body. The evaporation capacity, and hence the concentration of the product, is controlled by varying the speed of the compressor.
Condensate from the evaporator is recycled to the process reducing the quantity of fresh water required by the factory. There is an additional energy saving as this fresh water must be heated to the process temperature.
Continuing expansion created a need to increase evaporation capacity, but the existing boiler was already operating at full load on occasions. After considering several alternatives, Pure Malt Products decided to install a new falling film evaporator, which operates on the mechanical vapour recompression principle. In a steam-heated evaporator, all or part of the evaporated vapour is discharged to a condenser, and its large heat content is lost to the system. If the vapour is compressed to a suitable pressure, it can be condensed in the evaporator acting as the heating medium. The steam supply is largely replaced by the mechanical energy input to the compressor, and the overall energy consumption is greatly reduced.
The new evaporator at Pure Malt Products is a single effect, three-stage system. Operation is under vacuum, and the main components of the plant are shown in the figure. The feed to the evaporator enters the system through the plate heat exchanger shown on the right hand side of the figure. After being heated by process condensate, it passes to the vapour-liquid separator. From the separator it joins the circulating flow of the product in the first stage of the evaporator (on the right side of the falling film evaporator). Partly concentrated product overflows from the first stage to the second stage of the evaporator via an internal weir, and circulates around the second stage, which is in the centre of the evaporator. Product from the second stage overflows in a similar manner to the third stage on the left side of the evaporator. A separate positive displacement pump pumps the final product from the third stage. The evaporator is provided with a fully automatic control system, and is designed to concentrate several different products at a high efficiency. |
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Performance
| Energy | Since the commissioning of the evaporator in January 1999 a careful monitoring of utilities consumptions has confirmed the anticipated savings. At an evaporation rate of 4000 kg/h, the new evaporator uses a total of 85 kW for the compressor and all pumps, about 40 kg/h of low-pressure steam, and a small quantity of cooling water for the vent condenser. Comparing this with the operating costs for the steam-heated evaporator previously used indicates that the running costs are reduced by at least GBP 2 per ton of water evaporated. |
| Coefficient of performance (COP): | 38 |
| Test conditions: | Design operating conditions (without benefits of condensate recycle) |
| Heat pump cost breakdown | No data |
| Alternative system (if has been considered) | No data |
| Payback | No data |
| CO2 emissions | No data |
Operational experience and other comments
The compressor has received only routine maintenance on an annual basis since the commission of the evaporator. One drive belt failed after a few months of operation, but otherwise there have been no problems relating to the vapour recompression process. Mechanical vapour recompression can provide a cost effective alternative to steam heating for evaporators.
Contacts
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Contact 1: |
Fred Brotherton |
| Company: | Beedes Ltd |
| Role: | Process engineer |
| Address: | Malthouse Lane Burgess Hill, West Sussex RH15 9XA UNITED KINGDOM |
| Telephone: | + 44 1444 250708 |
| Fax: | - |
| Email: | Fred.brotherton @ beedes.co.uk |
| Last updated: 1 March 2004 |
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