In Nesle, France, CNIM EB has been operating a 240,000 tonne per year wood waste to energy plant on behalf of the facility’s owner AKUO Energy Since 2013. In July last year, to reduce the ongoing maintenance and cleaning routine it chose to install Shock Pulse Generators for continuous and automated online cleaning of finned tube ECOs in the biomass boiler.
CNIM’s Dr Nazim Merlo explains that the temperature after the ECO installation showed a saw-tooth profile (Figure 1). With a constant 100 t/h steam output, the flue gas temperature after the ECO went up 40°C from 140°C to 180°C within 10 days. The flue gas temperature drop through the ECO was 100°C with a clean module but only 50°C after 10 days of operation.
However, the temporary steam consumption of up to 10% of the plant’s total steam flow for each soot blower led to some issues with boiler control. In order to maintain a permanently high quantity of process heat and cooling water during the operation of the soot blowers, the steam flow had to be temporarily increased.
To reduce this maintenance routine, and its additional load on steam generation, CNIM, turned to Swiss company, Explosion Power GmbH, and its Shock Pulse Generator (SPG) technology. The system is an online boiler cleaning technology which automatically generates shock pulses through the combustion pressurised gas. The shock generated prevents the build-up of soot and slag inside the boiler and reduces the need for plant shutdowns for routine maintenance, as well as the parasitic use of steam.
Kaspar Ninck, Process Engineer at Explosion Power explains that in implementing the upgrade CNIM’s R&D team carried out a layout study and also participated in the installation and commissioning process.
There was no reference for the installation of SPGs on finned tube ECO bundles in biomass boilers prior to this installation. However, the trial and subsequent analysis of corresponding boiler data validated the efficiency of the equipment and allowed the optimisation of the Shock Pulse Interval.
The 16 MWel boiler installed at the plant is a “Single Pass” type while spreader-stoker is supplemented with ash-recirculation from the cyclone which allows the efficient combustion of natural wood by minimising the unburned gas rate.
From the furnace, the flue gases enter the vertical superheater and evaporation section and eventually enter the ECO pass, where two finned tube ECO bundles cool down the gases from 250°C to 170°C. Each ECO bundle has overall dimensions of 6.7 m length x 2.4 m width x 1.6 m height.
Due to the high-pressure wave absorption of the finned tubes, the most powerful SPGs were chosen right from the beginning. In July 2016 one TwinL and one EG10XL Shock Pulse Generator, which CNIM rented, were installed on the rear wall of the ECO pass between the two ECO bundles (Figure 1) and used with an Shock Pulse Interval of one hour. After commissioning the SPGs, the plant’s existing sonic horns could be stopped and the two soot blowers were rarely used (five to seven cleaning cycles per month).
The issue with the saw-tooth profile in figure 1 was solved with the Shock Pulse Generator cleaning. The outlet temperature on the ECO modules was stabilised with only fluctuations of only 20°C remaining. The cooling of the flue gas in the ECO modules was also stabilised at 80°C.
Following five months of operation, an inspection on the ECO units showed no additional abrasion or wear due to the pressure waves. In that time the Shock Pulse Generators were also permanently acquired by CNIM. The biomass boiler can now be operated continuously and without additional manual cleaning on the ECO units. An additional benefit is that the short-term increase of steam flow is no longer necessary, which has, in turn, has reduced slagging and fouling in the boiler.
According to Merlo, the installation has shown that Shock Pulse Generator cleaning technology can be implemented in this type of application with high efficiency on finned tubes, while protecting the boiler.