The Jämtkraft Lugnvik combined heat and power (CHP) plant has been processing forestry biomass into bioenergy since 2002. The plant converts about a third of the biomass into electricity and two-thirds into district heating that covers the needs of 90% of Jämtland county, which lies in the middle of Sweden.
Jämtkraft experienced issues with repeated leakage from the boiler blowdown heat recovery unit at its Lugnvik CHP plant and suspected that the cold makeup water was cyclic, causing temperature and pressure cycling on the heat exchanger. The company then turned to Alfa Laval to find a solution. Due to process temperatures above 200°C, gasketed plate heat exchangers were not an option, so after consultations with Jämtkraft, Alfa Laval recommended using the all-welded Alfa Laval DuroShell plate-and-shell heat exchanger designed for boiler blowdown heat recovery.
The advantages of the Alfa Laval DuroShell heat exchanger and a flash tank for heat recovery in the high-pressure, continuous blowdown steam system at the Lugnvik CHP are twofold. First, it recovers 130 kW from boiler blowdown to preheat the incoming makeup water, which results in significant energy savings. This is equivalent to recovering more than 1100 MWh on a yearly basis. Second, it reduces the drain water temperature, making compliance with drain discharge regulations easy.
Superior thermal efficiency, low installation costs, minimal energy consumption and reduced maintenance costs made investment in the DuroShell worthwhile for Jämtkraft. Karl Selander, Operation Manager at Jämtkraft, states:
Payback time for our investment in the Alfa Laval DuroShell was about two to three years. Apart from excellent heat recovery, we wanted a heat exchanger that required minimal maintenance, year after year. That heat exchanger is the Alfa Laval DuroShell.”
The Lugnvik CHP plant produces superheated and high-pressure steam. The steam is collected in a steam drum at a temperature of 540°C and a pressure of 145 bar. In the steam drum, continuous blow down, or the continuous removal of 1–2% of the water in the system, increases the water quality and prevents the formation of mineral deposits dissolved in the boiler water.
The temperature and pressure of this water is high and goes to a flash tank. From there, the separated steam goes back to the deaerator and the water at temperatures of more than 200°C is sent to the Alfa Laval DuroShell. The DuroShell recovers surplus heat from blowdown water by preheating the incoming makeup water, which is added to the system to replace the 1–2% that is continuously bled off.
This results in saving 400 tons of biomass each year. Reducing fuel consumption not only increases boiler efficiency, but also cuts emissions.
Robust and fatigue-resistant, the Alfa Laval DuroShell withstands the high process temperatures required for our biomass-fired CHP plant.
Karl Selander, Operation Manager at Jämtkraft
A patented plate pattern optimizes thermal efficiency with improved fatigue resistance, flow distribution and mechanical strength.
Patented design enables improved fluid distribution, mechanical strength and unparalleled fatigue resistance.