Tranter plate and frame heat exchangers (PHEs) recycle heat energy to district heating loop, helping increase thermal efficiency by 20%. Locked within urban waste streams lies a lifeblood of civilization...energy. It takes ingenuity to unlock and capture this potential without environmental damage or thermal inefficiency. SYSAV, an integrated waste management and energy company in Malmö, Sweden, is using Tranter plate and frame heat exchangers to capture waste heat from boiler flue gas condensate and cool this stream prior to purification and discharge. This flue gas condensation heat recovery process is providing SYSAV with attractive financial and environmental benefits. For a low upfront project cost, the company is obtaining a significant energy yield, with no increase in emissions.
Energy for district heating and power generation
SYSAV collects, recycles and treats commercial, industrial and household waste and garbage. The mission of SYSAV is to provide environment-friendly waste disposal and recycling and efficient waste-to-energy conversion. Recent tightening of EU emissions standards caused SYSAV to embark upon a major upgrade and expansion totaling 200 million SEK (U.S. $26 million). The scope included installation of a modern, four-stage wet flue gas scrubbing and heat recovery process by Götaverken Miljö AB serving two of the boiler lines. SYSAV also carried out upgrades to two of the waste-fired boilers.
The waste-to-energy plant operates three waste-fired boilers; all three supply heat energy to the Malmö and Burlöv district heating net. The newest boiler supplies steam for approximately 145,000 MWh/yr of electric power generation. Energy from the plant supplies about 40% of the district heating load, equivalent to the energy in 100,000 tons of heating oil, or enough to supply the annual needs of 80,000 three-room apartments (almost 1,000,000 MWh). An ongoing expansion will raise output to 50% of the district heating consumption.
The gas cleaning process takes place in a four-stage scrubber, which controls the discharge of ammonia, hydrochloric acid, sulfur dioxide, dioxin and heavy metals. The SYSAV system incorporates the proprietary ADIOX® dioxin reduction technology2 from Götaverken Miljö AB.
Hot condensate to district heating
SYSAV has been able to capture significant heat energy from the scrubbing process. When the flue gases are washed with water that is cooler than the flue gas’ dew point, condensation occurs in the top stage of the scrubber. Heat in the condensate is transferred to the district heating loop through a Tranter PHE model GXD-205 plate and frame heat exchanger. An in-line strainer at the flue gas condensate (hot) side inlet on the GXD-205 collects particulates carried along with the condensate. This tower packing material increases the contact surface between the gas and process liquid, improving the rate of acid and dioxin separation. During the exchange, the scrubber condensate is cooled to a temperature 1–2 °C (1.8–3.6°F) above the incoming district heating water.
Two other heat exchangers complete the condensate heat recovery and cooling process. A Tranter PHE Model GCD-016 heat exchanger uses district heating water as cooling media for the Stage 4 flue gas condensate. A GLD-013 unit uses ground water to further cool the Stage 4 water and also to cool process water from scrubber Stage 3, the sulfur dioxide step. The plates for all three units were manufactured in 254 SMOTM stainless steel (1.4547) to withstand chlorides and fluorides in the flue gas condensate.
Cooled process water goes to the water purification system and then to discharge. When the district heating plant is not operating, ground water alone is used in the GLD-013 to cool the Stage 3 condensate before it is pumped to the purification system.
Performance makes the difference
Götaverken Miljö project engineers selected Tranter PHE plate and frame heat exchangers over shell and tube heat exchangers for their costeffective performance within the constraint of high materials costs. Other factors were the units’ compact size that minimized footprint and Tranter’s technical solution and support.
Broad potential for savings
The flue gas condensate heat recovery strategy as employed by Götaverken Miljö at SYSAV has potential for any boiler flue gas stream 150°C (300°F) or above. By cooling the flue gas to below its dew point, it is possible to capture large quantities of energy during gas condensation. The efficiency can be further improved by inclusion of a heat pump. By recycling otherwise wasted heat energy, plants operating boilers with scrubbers can improve their overall thermal efficiency, with significant fuel savings.
Tranter PHE Model GCD-016 The heat exchanger transfers heat energy from Stage 4 flue gas condensate to district heating water.
Customer case
