As part of the H2020 DryFiciency project, an innovative dryer technology of Scanship has been integrated with a two-stage turbo-compressor steam heat pump system developed jointly by SINTEF and EPCON and installed at the test site of Lindum in Drammen, Norway. The innovative heat pump dryer can be used to dry different biomass types, such as bio-sludge, wood chips and garden compost.
MVR heat pump demonstrator
The heat pump system is an open loop Mechanical Vapor Recompression (MVR) system, which uses an advanced, low-cost turbo-compressor technology originating from the automotive sector, developed by Rotrex. It operates with water as working fluid – a natural, non-toxic, non-explosive refrigerant, that is reliable and available in abundance.
The MVR heat pump demonstrator (see Figure 1) aims at reducing the dryer’s energy consumption by up to 75% eliminatating the need for fossil fuel use in the dryer. The solution enables the recovery of excess steam from the dryer, which would otherwise be wasted. This is achieved by compressing the steam from ambient conditions (100°C, 1 bara) to 4.2 bara. The high-pressure steam from the compressor rig is then condensed in an MVR heat exchanger to supply heat to the steam to be used in the dryer (see Figure 1). The condensate holds around 140°C and can potentially also be used for other heating purposes.
Figure 1: Schematic diagram of MVR paddle dryer for sludge drying
Benefits
The demonstrator has achieved a capacity of 500 kWth and utilizes up to 1 ton steam per hour, while the MVR heat pump has sufficient capacity to support two driers. The rig was tested at various operating conditions, ranging from supply temperatures from 125°C – 146°C. Good performance was achieved with COP values from 4.5 up to 8.7 with (Carnot efficiencies of around 50%) depending on the temperature lift.
Key facts
| Dryer type | Super-heated steam dryer (paddle), with steam jacket |
| Drying product(s) | Dried biomass (bio-sludge, wood chips, garden compost with original MC around 70%) |
| Drying medium | Superheated steam |
| Operation | Batch, discontinuous |
| Product conveying | Paddle |
| Heating medium temperature | 125-140°C superheated steam at 1 bara |
| Heat sources | Boiler steam |
| Heat pump capacity | 0.5 MW |
| Flow temperature heat pump | 142°C (condensation temperature at 4.2 bara) |
| Refrigerant | R 718 (water) |
| Drying time | Approx. 10 h |
| Start of operation | 2020 |
| Capacity | Approx. 160 kg/h water evaporation (from 70% to 15 % MC) |
| Dryer dimensions | N/A |
| Outlet condition drying medium | Approx. 100°C saturated steam |
| Direct heat recovery | Yes |
| Heat source for heat pump | Outlet of dryer |
| Challenges | There were some operational start-up challenges to integrate the turbo-compressor heat pump with the steam dryer in terms of maintaining superheated steam coming from the dryer, which in turn reduced the capacity of the heat pump. |
| Tracked parameters | Temperature, COP, MC, weight |
More information
For further insights into the configuration of the open loop heat pump cycle, the sizing of the heat pump, and the turbo compressor prototypes used, please refer to the document here (from page 23 onwards)
Additional information on the integration, commissioning and operating phase of the novel heat pump dryer system is compiled here (from page 22 onwards).
Watch the DryFiciency open loop heat pump demonstrator here.