Feature : Distri ct energy – We do not talk about sustainability, we live it. Wood is one of the very few renewable resources in Switzerland and the sustainable and controlled use of forests is guaranteed. All the residual wood from the sawmill is used for modern heat extraction and supply, said Paul Aecherli, Owner and Founder of Aecherli Holz AG. Bioenergy International No 81, 5-2015 15 as the deadline fast approaches, one district heat operator has installed a novel dry electrostatic precipitator (DESP) future-proofing expansion and PM compliance. Located in Regensdorf in the Canton of Zürich, northeastern Switzerland, Aecherli Holz AG is a small, family-run sawmill and wood retail company. In business for over 50 years the company specialises in custom processing of hard- and softwood species sourced from local forests into a variety of components and products. In 1996 a new 1800 kW woodchip boiler, from Swiss combustion specialists Schmid Energy Solutions, was installed. This enabled the company to heat its dry kilns as well as supply heat to a newly built 426 cell correctional facility located 1 km from the sawmill. Network expansion During the period 2009 to 2013 the heating network was expanded to include two new developments; a new housing complex consisting of 125 apartments and a commercial property with 80 apartments and commercial retail space. To cope with increased heat demand a second Schmid 1800 kW woodchip boiler was installed in cascade at the sawmill as well as a 95 m³ buffer tank to ensure sufficient heat supply at peak demand. With the heat demand expansion, all wood residues such as bark, off-cuts, slabs, sawdust and shavings from the sawmill are used as fuel. Additional biomass such as logging residues, thinnings, right-of-way clearing and windthrow is purchased locally from the surrounding forests. Novel flue-gas cleaning As an existing wood-fuelled heat installation, larger than 500 kW but under 10 MW thermal rated input, Aecherli Holz will have to comply with PM ceiling of 20 mg/Nm³ by the end of 2017. In March 2014, Aecherli opted to be the first to retrofit its heating plant with a unique new flue-gas cleaning system, a multichamber dry electrostatic precipitator (DESP) developed by Swiss compatriots, IS SaveEnergy AG, a company specialised in developing and installing complete heat recovery and flue-gas cleaning solutions for wood-fired combustion plants. As with conventional ESPs typically used on large single boiler installations, particulate matter is separated from the flue-gas using an electrostatic charge. By charging the electrically neutral dust particles these are removed from the gas flow at the collecting electrode. In practice this can prove difficult and costly. – When a central flue gas cleaning system is installed downstream of a multi-boiler system, it has to cope with a large range of load variation which can be a challenge for conventional flue-gas cleaning equipment such as ESPs. Our multi chamber electrostatic precipitator automatically regulates the number of chambers through which the gas flows, depending on the volume of exhaust gas, said Thomas Graf, Product Manager ESP, IS SaveEnergy AG. Future-proof expansion and compliance According to Graf the novel multichamber feature enables flow speeds to be maintained even in periods of low-load operation. This translates into significant advantages in terms of ESP availability as well as operating costs for heat-led systems. – This is a key issue as Swiss law stipulates at least 97 percent ESP availability when the boiler is operating, explained Graf. At Aecherli Holz the compact tri-chamber DESP unit is installed over an existing container outdoors. A series of emission measurement results by an accredited institution in January this year suggest that the Saveenergy DESP does indeed perform well even under variable boiler load and resulting flue-gas volume. Fuel: woodchips/bark @ 50% mc Boiler load: 15% - 95% @ 3000 - 19000 Am³/h Flue-gas temperature: 95 °C - 145 °C Inlet dust load: 135 mg/Nm³ @ 11 vol-% O₂ Emission (max 20 mg/Nm³): 4 – 9 mg/Nm³ @ 11 vol-% O₂ Temperature lost over DESP: 3.5 °C Pressure lost over DESP: 190 Pa – Currently the DESP installation is using two of the three chambers. The third chamber will be activated once a planned thermal capacity upgrade is executed, said Thomas Graf. Today the Aecherli Holz heating plant replaces around 1200-1400 tonnes of oil per annum. According to owners, Paul Aecherli and his daughter Celine Hartmann-Aecherli, local interest in district heating has prompted plans to increase the thermal capacity of the plant to 5 MW in order to expand the network. – We have already ordered a new 2.4 MW Schmid boiler to replace Future-proofing expansion and compliance Although not a member of the European Union (EU), Switzerland has adopted stricter air emission regulations similar to the European Air Quality Directive 2008/50/EC. Known as LRV regulations the new rules include lower thresholds for particulate matter (PM) for existing facilities and they come into effect 1st January 2018. the oldest 1.8 MW one and it will be installed during the autumn. The EUR 300 000 investment in the DESP has already future-proofed emission compliance of the expansion, said Paul Aecherli. The plan is to replace the remaining 1.8 MW boiler with second 2.4 MW boiler within the next two years bringing the total thermal capacity of the heating plant to just under 5 MW. Text: Alan Sherrard BI81/4869/AS Photo courtesy Saveenergy Photo courtesy Aecherli Holz
Bioenergy no 5 September 2015
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