Introduction

In 1997, the Council of Molins de Rei, Entitat Metropolitana de Servesi Hidràulics i Tractament de Residus (EMSHTR) and Institut Català d’Energia (ICAEN), through their affiliated company Efiensa, formed Molins Energia, SL.  The above three public organisations called for a tender in 1999 in order to select a private company that would become part of Molins Energia, SL and would take care of building and managing the plant.  This public tender was awarded to a grouping of companies formed by Hidrowatt, SA and Companyia d’Aigües de Sabadell, SA, gathered under the following name: Biomassa Aprofitament Energètic, SL.

Objectives and target audience

The aim was to build and keep a heat generation plant operative, run on biomass, as well as to supply hot water to 695 newly-built dwellings in La Granja residential area, Molins de Rei, thanks to a District Heating grid.

Financial Resources and Partners involved

The project received financial support from the European Commission -within the  framework of Thermie European Programme-, from the Spanish Ministry of Industry and Energy –PAEE Programme- and from the Directorate General for Energy and Mining of the Catalan Government. The overall investment, including the supply grid cost, was 1,622,000 Euros (270 Million Pta), of which 456,700 (76 Million Pta) were subsidised.

Process

The main elements included in the heat plant are: a biomass boiler with 2,250 kW of thermal power (this boiler is prepared to generate hot water after combusting solid fuels), 3 natural gas modular boilers (used to support the biomass boiler should there be stops or consumption peaks).  Biomass -mainly almond shells, chipped pine cones and forest kindling- reaches the plant on lorries, which unload it in a 180 m3 silo.  This size provides the boiler with operative autonomy for 55 hours at full power.  The silo has a moveable bottom formed by three non-finished bolts in series, which are activated by electrical engines to guarantee the input of biomass in the boiler’s combustion chamber.  The combustion chamber has a water-refrigerated moveable grate where biomass undergoes a two-stage combustion.  To start with, organic matter is dried as fuel advances through the chamber’s moveable grate -this is the process when volatile compounds come off-and combustion is later completed with the intake of secondary air.
The biomass boiler sucks gases from the combustion chamber and makes them flow three times through the boiler so that they yield their heat until reaching 160O °C temperature. This way, before they are ejected into the atmosphere, they go through a high-efficiency multi-cyclonic sensor that separates small-sized particles from the gas flow.  The hot water generated in this process is stored in two 100 m3 tanks during the hours the plant is in operation.  From these tanks, water is pumped to the supply grid at a 2.5 bar pressure by means of a system composed of three centrifugal pumps.  The storage system is only kept operative during the daytime -16 hours per day-, so that the hot water stored in the tanks guarantees the dwellings own heat demand overnight.  This system automatically adjusts the delivery of water to be pumped depending on the current energy demand so that the powered water temperature can be maintained constant at 90 °C.  The supply grid is almost 2,400 m. long.  It is formed by stainless steel pipes with diameters ranging 60 to 273 mm.  These also have a polyurethane coating which enables hot water to practically bear no temperature loss along the runoff.  Each dwelling has a small-sized and compact facility in its kitchen or laundry room, which is composed of two heat exchangers where hot water from the supply grid yields its heat to the dwelling’s heating or hot water generation system.  Each dwelling was furnished with a calorie meter to gauge the flow and temperature jump between hot water intake and outlet.  This allows ready information on energy consumption at any time.  The meter also has a communications bus to enable readings from the plant’s control room.

Results

The hot water supply service at Molins de Rei plant was operative by February 2000. Initially, it was run on natural gas boilers.  The biomass boiler started its operation in January 2001 and it is currently at full operation as previously scheduled.
There are presently 250 dwellings being serviced with heating and sanitary hot water and it is envisaged to have connected 695 dwellings to the grid by the year 2003.
Up to November 2001, the plant had consumed 500 tonnes of biomass, with a useful-heat
production of 1,540 MWh.  This consumption accounted for saving 165 toe of fossil fuels and for preventing some 380 tonnes of CO2 from being dispersed.  Once the remaining dwellings have been connected until meeting the foreseen 695, biomass consumption will be in the range of 2,200 tonnes/year and heat production will be 6,800 MWh/year.  This will imply saving 730 toe/year and stop 1,700 yearly tonnes of CO2 from being dispersed.

Critical Success Factors / Challenges

Some important lessons can be learned from the main elements characterising this project.  First of all it is important to underline how the collaboration and commitment of public institution and private initiatives are key factors for the success of a similar initiative. It is still very difficult that a RES or RUE project at sub-urban level like this one (a district biomass heating system) could be conceived and developed only by a private Company, because some initial extra costs of the plant, together with the fear of offering a “non- standardised” product (biomass heated houses, in this case) clearly prevent building contractors to adopt these solutions. Within this project, the opportunities offered by public co-financing ( easier in the case of public housing promotions) have largely contributed to overpass this obstacle and to favour the implementation of an innovative housing concept which could largely influence similar initiative at local or regional level specially where some fuel collection conditions could be met.  This clear public commitment (specially at City Council level) provokes also a very high multiplier effect in terms of impact of citizens attitude towards environmental/energy saving issues.  A second positive element to be considered is in the special attention given to encourage user’s participation to the house energy management, by the design and installation of user’s friendly devices within each of the houses served by the district heating network and also by the general but technically correct information given about the functioning of the whole system. By the mean of those two activities the involvement of the population of the area, was ensured since the beginning and represent a crucial factor of a growing of common environmental consciousness.