The heating for the village is produced in a central boiler house. The boiler house is equipped with two boilers. One boiler has duel fuel capabilities, both wood and oil, and the second boiler for peaking and standby oil firing only.
The wood fired boiler is fully automatic from fuel in-feed to ash removal. The system has built-in telecommunications modem for remote troubleshooting and supervision. If the wood supply becomes limited due to severe weather conditions, the boiler can be operated on oil.
The boiler house is also equipped with a standby generator to enable the complete system to operate during longer power failures.
Fuel: Wood Chips (Biomass)
The combustion system is designed for a variety of different biomass fuel characteristics. It can handle and burn any wood waste from bark to sawdust, green to kiln dried. Presently, the wood is received from the Barrette-Chapais. Ltd. sawmill approximately 26 km from the village. The wood waste used in the heating system would otherwise have been stockpiled at the sawmill.
Investigations regarding establishing a fast growing energy forest for the site is underway. The plantation would create some local employment while also enhancing the habitat for the wildlife of the area.
Backup Fuel: Oil
Fuel oil will be used for peak load and for backup purposes. The oil will be a special arctic type that has a very low freezing point. The fuel tank has a capacity of 50,000 litres and will enable the system to operate at design conditions for several weeks.
Material Handling System
The wood waste is collected from the sawmill with one of the Oujé-Bougoumou-owned trucks. After off-loading in the fuel storage all functions are completely automatic. A hydraulic stoker reclaimer system feeds an auger system into a metering bin prior to the combustion chamber. The fuel handling system has a built-in backfire protection system that requires no power to operate.
The automatic combustion system is a self-contained unit. The fuel is fed from the metering bin with an auger to the sloping moving grate combustion chamber. The combustion chamber is heavily insulated and refractory lined enabling the use of high moisture content fuel. The design also minimizes the amounts of unburnt hydrocarbons and fly-ash. The ash is collected and handled automatically in the combustion chamber in a dry system totally enclosed and removed to outside storage containers with a set of screw conveyors.
The combustion chamber is designed to handle a variable load on the district heating system and modulate from a standby mode to full load automatically depending on the energy usage in the village.
Wood Burning Boiler
The boiler or heat-exchanger for the wood burning system is placed on top of the combustion chamber. The boiler is a scotch type fire tube three pass system. The boiler is designed and manufactured in Nova Scotia.
The dedicated oil-fired boiler is also of a scotch type fire tube design, however, this has a wet back. This type of boiler was selected for high reliability and very little maintenance requirement.
Both the wood burning boiler and the oil-fired boiler are supplied with the same type of burner. The burners have a full modulation firing sequence. The burner on the wood fired installation is mounted on a door and can be put in operation within minutes if the wood burning system fails or the fuel supply is limited due to severe weather conditions.
The emissions from the system built in Ouje-Bougoumou will reduce the production of nitrogen oxides by approximately 35% or 160 kg the first year compared with an oil-fired system. The emissions of carbon dioxide will be 0 in comparison with using fossil fuel as there will not be any additional carbon dioxide added as the wood binds the equivalent of carbon dioxide during its growing as well be released during combustion. It is estimated that during the first year more than 200 tons per year of carbon dioxide will be avoided. The wood burning system is designed to meet the most stringent environmental standards in North America.
The ash produced in a wood fired system as installed in Ouje-Bougoumou consists mainly of the trace minerals the tree has taken up from the soil during its growing process. The ash is alkaline and will act as a fertilizer for existing reforestation, the planned energy plantation, and for a possible future greenhouse heated by the excess capacity of the system. Being alkaline will also minimize the effects of the acid rains from the south.
The district heating system uses the most modern variable speed pumps available on the market today. This has several consequences including the minimization of the use of electric power for the pumps. No more water will be pumped than required to meet the load of the district heating system at any given time. The variable speed system will operate on both pumps and have an automatic start-up after power failure. If the variable speed drive controller fails, the pumps will automatically switch to normal operating mode for optimal reliability of the system.
Hot water will be supplied at different temperatures depending on the outdoor temperature and increasing up to 90 degrees C at design temperature. This control strategy is developed to minimize distribution losses. The control equipment is located in the boiler house.
The boiler house will be unmanned but is supplied with an automatic dialer that will alert an operator on site if required.
In the boiler house an energy meter is installed for the overall monitoring of the energy usage of the system. This meter will be used for overall correction of the individual meters in each building. The meter is a magnetic flow type with the highest possible accuracy.
The piping distribution system consists of an underground hot water distribution network with supply and return pipelines in a closed circuit. Each building is connected to the network via a customer heat transfer station that regulates and measures the energy taken from the distribution system. Each building is directly connected to the distribution system.
The system is designed to distribute hot water to all buildings. The distribution system is unique for Canada in several ways. It utilizes a combination of plastic (cross-linked polyethylene-PEX) and steel. All pipes have been factory insulated with a freon free polyurethane. Protective cover of the pipes are high density polyethylene. The steel pipes have been welded together and include special pipes with compensation.
The steel carrier pipe and the jacket are fixed in relation to each other through insulation. The expansion of the system is restrained by the friction of the earth on the jacket and with built-in stress reliever pipes. All joints are sealed with double seals.
The flexible plastic pipe has been designed especially for small-scale district heating systems with low heat density. Savings in both materials and installation costs provide significant cost benefits when new pipe installation techniques are used.
The main advantages of the plastic and copper options are flexibility and corrosion resistance. The plastic used is a visco-elastic material, with the internal stress caused by temperature changes absorbed by the material. Expansion loops or joints are not normally required .
The flexible plastic pipes were delivered in rolls up to 100 m. The flexible plastic pipes have been used for all branch lines. The carrier pipe is made of cross-linked polyethylene (PEX) and also has an organic oxygen diffusion valve. The jacket pipe is made of polyethylene (PEL). Semi-flexible polyurethane with very good insulating properties is foamed between carrier pipe and jacket pipe in factory. The pipes have been joined together with press couplings.
The distribution system has been designed for 90 degrees C maximum temperature. The maximum pressure allowed in the system is 90 psi. All components have been pressure tested for 1.5 times maximum operating pressure prior to backfilling.
Each building is supplied with outside shut-off valves for added security. If a house would be catastrophically damaged the district heating can be closed off to minimize disturbance to the rest of the system.
The distribution system for the village has been designed with optimization in mind. The size of the pipes varies depending on the number of presently connected houses and future expansion in the area . The largest pipes coming out of the boiler house have a diameter of 180 mm and go down to the smallest size of 32 mm.
Total Pipe Length, Steel
Total length of steel pipes constructed in 1992 is nearly 600 meters.
Total Pipe Length, Plastic
Total length of plastic pipes constructed in 1992 is nearly 2,300 meters.
Consumer Heat Transfer Stations
The buildings' hot water system is connected to the district heating system via a heat transfer station located in the basements.
Each heat transfer station consists of a prefabricated heat exchanger unit for hot water heating. The heat transfer station is provided with the necessary control equipment as well as all the internal piping. The heat transfer station is designed for ease of connection to the buildings' internal heating and hot water system.
The prefabricated heat exchanger units for domestic hot water are especially designed for single-family residences and for small multi-family residences. They consist of brazed plate heat exchangers and self-actuating control valves.
The heat transfer unit is mounted on the wall in the basement above the possible future location of a clothes dryer. No hot water tank is required and hence no floor space is required for the complete heating system including domestic hot water production.
Hot water is circulated through the radiators that are mounted underneath the windows throughout the building and interconnected via pipes laid in the subfloor or mounted on the wall. The radiators are fitted with thermostatic self-contained valves for individual room temperature control. A sub-circuit with a separate pumping system is direct-connected to the primary system.
The sub-circuit operates with a constant flow rate and the supply water temperature is controlled by a self-acting control valve in the single family houses and control unit with outdoor temperature reset for larger buildings.
Each heat transfer station is equipped with an energy meter for individual billing of energy used. The energy bills will be similar in appearance to a typical utility bill.
Duncan Varey, our District Heating Coordinator, calculated the comparative costs of producing 1.0 MW of heat for biomass, oil and electric. This is what he found:
- to produce 1.0 MW of heat utilizing electricity from Hydro Quebec at their (current) 1993 rates costs $71.80.
- to produce 1.0 MW of heat utilizing oil at approximately 25 cents/litre costs $30.64.
- to produce 1.0 MW of heat utilizing our source of biomass, the sawdust from the nearby sawmill, costs $2.44.