The first biomass-fired district heat network in Spain using high temperature thermal oil has recently been commissioned. Located in Berga, Barcelona the commercial heat plant is already supplying high temperature energy to several local industries.
The project involves the installation of two 2.3 MW biomass-fired thermal oil boilers. Heated to 300 °C, the thermal oil provides energy to several industries in La Valldan industrial estate via two networks; a high-temperature network based on the thermal oil and a second conventional hot water network. It is a first-of-its-kind system in Spain.
“0 km” renewable energy
The project has been promoted by “Mancomunitat de Municipis Berguedans per la Biomassa”, a consortium of seven villages in Berguedà county, as a way to enhance their forest resources and create local jobs. Between them the seven villages (Berguedà-Gosol, Gisclareny, Saldes, Bagà, Cercs, Berga and La Pobla de Lillet) have 20 000 inhabitants of which Berga is the largest. The boilers are fuelled with woodchip all of which is sourced from Mancomunitat and this entity directly manages the “forest to furnace” supply of woodchip to the plant and administrates the energy supply to the customers.
Moreover, the contractor is a joint venture (JV) formed by Montajes Rus and Bover Installacions, which along with the construction manager -Engineering DosBes- are all local companies. Thus, a local virtuous circle connects resources and demand; a true “0 km” renewable energy project as Miguel Angel Sobrino, forest engineer designated by the regional government –la Generalitat- to support the consortium in the management of their forest resources, puts it.
Two energy lines
In its first phase, the project will provide energy to four companies via the two networks: the first one is 700 m long with thermal oil at 300 °C and 18 bar; and the other is 1.4 km long and supplies hot water at 90 °C.
To generate the heat two Eratic thermal oil boilers provided by the Innergy Group have been installed.
Robust equipment with sophisticated monitoring
The thermal oil boilers have a cylindrical-vertical burning chamber with refractory – Subterm type- prepared to burn woodchip up to G100 size. The fixed grate furnace lowers the final cost of the installation but requires a good quality woodchip.
– The difference with other similar boilers lies in the sophisticated PLC control system that we developed. This enables performance optimisation of the boilers, even straightforward standard boilers like these, explained David Moldes, Group Manager for Innergy, a leading automation specialist company in Spain.
The boilers are equipped so that they can be monitored and operated remotely; automatic ignition; bottom- and fly ash recovery systems; continuous monitoring of the oxygen level in the combustion chamber; regulation by frequency inverters fan, impeller and exhaust and intake auger.
High energy network
A pump moves the thermal oil from boilers to collectors, from where it can continue directly to the final points of consumption through the high temperature thermal oil network and a Vahterus heat exchanger oil-oil. Thermal oil also heats the water through a compact Vahterus oil-water heat exchanger located inside the boiler house. In this case, a Calpeda glanded pump -model NR50-125 / A-, leads the water at 90 oC to a 10 m3 Valinox buffer tank, from where it is distributed via two circuits to the water-water heat exchangers located at the consuming industries.
Should an industrial client require superheated water, it would be necessary to install an oil-water heat exchanger at the point of consumption.
Oil under pressure
Two different systems have been used to build the two networks. The thermal oil line needed radiographed welded pipes, whereas the hot water line, Victaulic pipe was chosen. The latter system with grooved couplings, fittings, and valves enabled quick assembly and has inherent expansion absorption capacity thanks to its system of couplings and joints that withstand temperatures up to 120 °C. The oil expansion tank, manufactured by the Innergy Group, is located inside the boiler house; it is pressurized with nitrogen to overcome the height difference with the highest point of the installation.
The consumer located above the level of the boiler house is at a distance of 700 m and a height difference of 55 m, making it necessary to work with an output pressure of the pump of 18 bar. The total volume of oil in boilers and network is around 30 m3.
Albert Bover, a technician with Bover Installacions and Alfonso Bermudez, a technician at Montajes Rus, both agree that the trickiest part of the project is the distribution of oil at that high pressure. Therefore they decided to use an extra thick pipe wall, 6.55 mm thicker than specified in the applicable regulations.
100 percent redundancy
The oil line is housed inside a 1.80 m walkway that allows access to any point on the network for control and maintenance. In addition to the control system of the boiler, the entire installation including the woodchip silo has a comprehensive monitoring.
– This is one of the strengths of the project, remarked Albert adding that energy meters have been placed at each point of consumption to facilitate billing process.
– To ensure continuous supply at all times, all elements of generation, pumping, and accumulation are duplicated, explained Alfonso. A business that wants to connect to either of the two heat networks must extend a connecting line from its facility to a connection point, where the contractor has placed the heat exchanger and the energy metering system.
Mobilising the public forest resource
A unique project like this also required a unique building: the housing for the heat plant has been built using a concrete and laminated wood structure “emphasizing the forestry aspect” as Miguel Angel Sobrino said. Adjacent to the building is the semi-submerged woodchip bunker that holds around 131 m3.
The annual woodchip consumption for the plant is estimated to be around 3 500 tonnes and is specified as G100 in size at 30 percent moisture content (MC). The woodchip is sourced from the forests under Mancomunitat’s jurisdiction. The standing timber is not auctioned to the highest bidder, which is unconventional in a Spanish context. Instead, a timber stand is first classified in situ before harvesting and then graded post-harvest allocating wood to different industrial end-uses. In this way Mancomunitat strives to optimize the economic performance of its forest resources.
Guaranteed wood chip
Mancomunitat is directly responsible for providing the woodchip to the plant and administrating the energy supply to end-users industries acting as a true energy services company.
The contractor JV is responsible for plant operations and maintenance (O&M) for the first four years. After this time, it is likely that management will be carried out through a new contract with a specialist company.
The cost of the heat plant project, excluding civil works, has been around EUR 1.3 million. The new activity generates four direct jobs in plant operations and maintenance (O&M) and 6 new jobs in the forest. Barcelona Provincial Council has contributed EUR 1.5 million to the project through a grant. The Generalitat de Catalunya has performed collaboration in different processes of the work.
In addition to the commercial heat project on the Valldan industrial estate, the consortium is completing the installation of 13 municipal biomass heat plants with a total installed capacity of 4.3 MW.
– Both projects complement each other as it guarantees continuous demand for biomass throughout the year and allows for better resource and work planning, explained Miguel Ángel.
The annual allowable cut in the forested mountains of Mancomunitat is 13-15 000 tonnes. Of this, 5 000 tonnes will be transformed into woodchips: 3 500 tonnes for the commercial heat plant and the balance as fuel for the 13 biomass boilers installed in the villages.
Text & photos: Ana Maria Sancho
This article was first published in Bioenergy International Español