Gas turbines are the most used technology in CHP systems, but it can also be used in power-only generation. They produce high-quality exhaust heat that can be used in CHP systems to reach overall efficiency of 70% to 80%. The most efficient technology for power-only production is gas turbine-steam turbine combined-cycle plant where efficiency can go up to 60% of the fuel LHV [9], while

simple-cycle gas turbines for power-only production can reach 40% of the fuel LHV.

Gas turbines are considered to be one of the cleanest ways to produce electricity. Because of their high efficiency and natural gas as primary fuel, this technology emits less carbon dioxide per generated kilowatt-hour than any other fossil technology in commercial use. This technology found wide application in oil and gas industry where gas turbine is used to drive pumps and compressors. In process industries, they are used to drive compressors or other large mechanical equipment, while many other industries use turbines to generate electricity on site. When used for this purpose, gas turbines are usually used in CHP mode where energy in exhaust gases provides the thermal energy. Gas turbine systems operate on the thermodynamic cycle called Brayton cycle. In this cycle, air is compressed in a compressor, heated in the combustion chamber and then expanded in the turbine. Part of the power produced by turbine is used for the compressor. Ideal Brayton cycle is showed in Figure 2.

A schematic of a gas turbine-based CHP system is shown in Figure 3. An air intake system supplies compressed air to the compressor. This air is directed to the combustion chamber where it mixes with the gaseous fuel in the required quantities. The hot gases from the combustion chamber expand through the turbine,

this operation is followed by the creation of a large amount of mechanical energy that drives the turbine rotor. The turbine shaft is connected to the compressor and generator at the same time. In the outlet flow, there is an additional combustion chamber where the temperature of the exhaust gases is increased according to the process requirements. The heat recovery boiler uses the heat from the exhaust gases to produce steam or hot water which is then used in a district heating system or other industrial processes.

Microturbines are small electricity generators that use fuel to produce high speed rotation which is transformed to electricity in a generator [12]. They use a variety of gaseous and liquid fuels. It is a relatively new technology which started to be commercially used in 2000. Origins of this technology can be found in automotive industry in 1950’s when turbochargers and turbo compressors started to be used in automobile engines.

This technology is able to provide a stable and reliable power supply with low emissions. It is ideal for distributed generation because of microturbine’s flexibility in connection methods and ability to be connected parallel in order to give higher output power. Microturbines are used in financial services sector, data processing and telecommunication, hotels and restaurants, residential buildings, office buildings and in other commercial sectors. Because of the wide range and low quality of fuels that can be used in this technology, microturbines are used in resource recovering operations in oil and gas industry, coal mines and landfill operation where they use by-product gas. When used in cogeneration, waste heat from microturbines is used for the water heating, building space heating or to drive ventilation system of the building [13].

Microturbines operate on the same principle gas turbines do as they basically are small gas turbines, so they use Brayton thermodynamic cycle. Most of them have internal heat exchanger that is used to preheat compressed air, which is called recuperators. Centrifugal compressor compresses the inlet air which later goes to the recuperator. After that, preheated air is mixed with the fuel in the combustor and hot combustion gas expands through turbines. There is one-shaft model that has a generator, compressor and turbine on the same shaft, and two-shaft models which have one turbine that drives the compressor, and the second to drive the generator. As the generator shaft is rotating at high rotation-per-second, high frequency generator produces AC electricity which is rectified to DC and then inverted back to AC with the frequency of 60 HZ for the U.S. market or 50 HZ for European market. Figure 4 shows a scheme of single shaft microturbine CHP system.

Unlike the other technologies used in CHP systems, steam turbines are independent from the type of fuel because they do not use the fuel directly [14]. Chemical energy of the fuel is transferred to heat energy in steam boilers in combustion process, after which is used to heat water and turn it to a high temperature steam. Steam is then expanded through the steam turbine where its pressure and temperature drop, while steam energy is transferred to mechanical energy on the steam turbine shaft. After the steam turbine, low pressure and temperature steam go to condenser where the heat is taken away and steam is turned into liquid. From the condenser water goes to pump which raises its pressure to the turbine’s inlet pressure. Steam boiler firstly heats the water to the bubbling point, then evaporates it to the steam phase line, and then heats the steam to the steam turbine inlet temperature. These three phases are done in the steam boiler components that are called economizer, evaporator and superheater. Thermodynamic cycle which is used in the steam turbine plants is called Rankine cycle [15].

Even though steam turbine price is competitive with other prime movers, the whole system which includes a steam boiler and other equipment has quite a high price per in-stalled unit of power. This is why steam turbine CHPs are well

suited for medium and large-scale applications, especially if there are inexpensive fuels available, such as biomass, various solid waste and by-products, refinery oil and gas. In CHP systems, heat can be extracted and used in many different ways. One is using a back-pressure turbine where the expansion is interrupted at some point, other is using an extraction-condensing turbine where one part of the steam is extracted and then used, and there is possibility to produce steam and hot water for the heat directly in the steam boiler. Figure 5 shows systems with the back-pressure turbine and the extraction-condensing turbine.

Internal combustion engines are a well-known and widely used technology, especially in the transportation sector. They are as well used for power generation, usually for the standby and emergency power, peaking service, intermediate and baseload, and for combined power and heat generation. There are two types of internal combustion engines: spark ignition (SI) and compression ignition engines (CI). Spark ignition engines used for power generation usually run on natural gas, but they can also use gasoline, propane or the landfill gas. Compression ignition engines, also known as diesel engines, use diesel or heavy oil fuel. They were very popular in power generation, but nowadays they have very limited application because of the emission concerns [17] [18] [19] [20]. Internal combustion engines are very well suited to a variety of distributed generation applications. They have a good partial load efficiency, high reliability, and they start quickly. If we also consider the fact that this technology is relatively low priced and it is very easy for maintaining and operating, there is no wonder why it is used worldwide.

Internal combustion engines operate on Otto and Diesel thermodynamic cycles. The main difference between these two cycles is in ignition, so in Otto cycle engines, there is a device that makes the ignition spark, while in Diesel cycle engines, the fuel ignites when compressed. Mechanically, these two engines

are quite similar: Fuel is ignited and combusted in the cylinder with the piston which is connected to the crankshaft which is transforming linear movement of the piston to rotation.

In CHP applications, the internal combustion engine waste heat can be used from four different sources: exhaust gas, engine jacket cooling water, lube oil cooling water and turbocharger cooling. This heat recovered from internal combustion engines is suitable for the low temperature processes, space heating, portable water heating, or for driving absorption cooling systems. Figure 6 shows how waste heat can be used in the internal combustion engines.

Fuel cells technology has a totally different approach to energy production then the other prime movers mentioned above. Like the batteries, fuel cells produce direct current electricity (DC) trough electrochemical processes without the direct combustion of fuel.

Two electrodes, a cathode and anode, pass the charged ions to electrolyte to generate electricity and heat [22] [23] [24] [25]. This technology offers a clean, quiet and efficient power generation. Since there is no combustion, there are no direct emissions associated with this technology. Fast development of this technology started 40 years ago as the fuel of the future and currently, some fuel cell systems are already available for the commercial use. However, these systems face competition problems such as low energy density, expensive materials in use for their production, system complexity and unproven durability and reliability. Because of these problems, it is very hard to ensure funds for their development and production, but as this technology is proven to be environmentally friendly and highly efficient, there are many incentive programs that can help mitigate their cost level.

Fuel cells use hydrogen as the most common fuel. Hydrogen is usually derived from hydrocarbons such as natural gas and then used in the fuel cells. Most of the fuel cell systems have three main subsystems:

1) The fuel cell that generates direct current electricity;

2) The fuel processor that converts natural gas to hydrogen;

3) The power conditioner that process electrical energy into AC or regulated DC.

As the production cost of the fuel cell technology is high, they are often used in CHP systems in order to achieve higher efficiency [27]. Waste energy is usually used for the district heating applications. Figure 7 shows the scheme of one fuel cell CHP plant.

Local thermal production, using diesel generators, mainly supplies electricity and heating to customers. According to [36], the Port-menier power plant is responsible for high emissions of CO₂ annually. For the purpose of design of power plant, peak values of heat and electricity were used. The data from 2016 show that the maximum electricity demand was at 1.2 MW. Figure 10 shows the heat and electricity load of the Anticosti community in 2016. This work is focused on the feasibility study of a biomass cogeneration plant to replace the diesel plant with a heat network.

The daily fuel consumption (diesel) is between 7200 l/d to 8000 l/d which corresponds in money to 10,368 CAD$ to 11,520 CAD$ per day. The plant has three generators (2 × 855 kW and 1 × 1135 kW) individually capable of supplying

almost all the electricity required for the proper functioning of the Menier port. The diesel power plant consumes between 1,200,000 and 1,500,000 liters of diesel annually and produces 2845 MW. Hydro-Québec forecasts an annual increase in subscriptions of 1.3% due to the number of inhabitants that increases during the summer season (hunters, tourists, hikers, etc.). The power plant meets the needs of the inhabitants and organizations of the port Menier, a consumption of 4.5 GWh, the rest is released in the form of heat and gas in the air (not used).

In the proposed case, it is a cogeneration plant operating on biomass (chips and bark), it will produce electricity and heat to supply the heating network with hot water. As shown in Figure 11, the plant operates with Rankine organic cycle units. To meet the electricity demand, the plant must produce 2.2 MW (2 units of 1.1 MW) from biomass combustion, in which case the biomass plant will replace the diesel plant.

The cogeneration plant will be equipped by:

· Two ORC cogeneration turbogenerators with a net capacity of 1.1 MW each.

They are supplied with thermal oil from the boiler at a power of 5140 kWh to produce electricity and hot water.

· A thermal boiler with a power of about 11 MW and an inlet temperature of 253˚C and an outlet temperature of 313˚C. The boiler operates on biomass, especially chips and bark, with a moisture content that varies between 25 and 60%. The most appropriate type of boiler is the mobile grate furnace boiler which is able to burn any type of biomass with a moisture content ranging from 10% to 60% for a power ranging from 400 kW to 25 MW.

· A biomass conveyor.

· An induced fan, with motorization and variable speed drive designed for high temperature and which conveys the combustion gases leaving the dust collector to the chimney.

· Ash extractor and conveyor to remove ashes to the outside.

· Ash plan.

· Chimney and gas pipes.

· Multi-cyclone type dust collector.

· Main power supply panel and control equipment panel with operator interface.

Energy demand and consumption in the village of Port-Menier is stable over several months of the year and does not exceed 1.1 MW except in December, January and February when the peak loads reach 1.5 MW. With the heating network the electricity demand decreases by 0.4 MW (see Figure 12).

The selected turbogenerators are Turboden TD10 CHP type, they equiped with a turbine, an asynchronous generator, a condenser, an evaporator and a regenerator, they are built by Turboden/pratt & whitney. The ORC process operates in a closed cycle with thermal oil for a required thermal power of 5250 kW for each 1.1 MW unit. The thermal output of the ORC unit is 4130 kW to the condenser, this energy is sent to the district heating network.

The technical data in the following Table 3 are based on an ambient temperature of 15˚C with a biomass of 40% moisture at a calorific value of 2.5 kWh/kg.

The calorific value of biomass is set by RETScreen at 19.8 MJ/kg for wood and eqaul to 5.4 kWh/kg. Table 4 represents the different characteristics of electricity and biomass consumption.

Despite its small population and remoteness from major centers, Port-Menier village has all the services necessary for the daily activities of its residents. The number of dwellings occupied by residents is 122 plus 60 detached houses, making a total of 182 residential dwellings. The heating network circuit must be able to meet the needs of the inhabitants for hot domestic water and space heating.

The entire network is divided into four main sections, the first section represents all houses and private dwellings (182), the second section represents the entire Saint-Joseph school and community radio, the third section represents offices,

and the fourth section represents the CLSC hospital. According to the 2016 census profile, the number of private dwellings is 182 compared to 218 inhabitants. The heating network will cover the heating needs of the inhabitants with a production capacity of 4130 kW and a total length of pipes reaching 9750 m. The total investment cost on the heating network is $14,941,614. Table 5 covers all expenses during the work, labor, equipment and piping.

The RETScreen renewable energy management software has calculated the model for the heating network (Table 6). The RETScreen database contains the technical data of the piping according to Canadian standards.

The RETScreen model calculates the section and length of the pipes according to Canadian standards and thus calculates the price of the pipes according to standard costs. Table 7 shows the dimensioning and cost of the main line pipes.

The model provides a summary of the dimensions (diameters) of the main distribution line pipes and the related costs.

To define the costs of the various equipment of the cogeneration plant, we used

the results of the articles cited in reference [37] [38] [39] [40] which are focused on the technical-economic study of Rankine’s organic cycle in order to produce electricity and heat. The results allowed us to make Table 8, we also take the results of the articles as a reference and basics for defining the limits and validating the results.

The financial analysis is an in-depth examination of investment costs, fuel costs of the proposed case, multiple expenses, total saving and annul revenues. The RET Screen clean energy management software has a spreadsheet called Financial Analysis, which simplifies the project evaluation process. Through the input data of financial parameters (discount rate, debt ratio, etc.), simple return, net present value (NPV). The financial analysis provides decision-makers with the financial parameters useful for their analysis.

Forest fuels are regarded as by-products of traditional forestry where tops and branches are harvested simultaneously with high-quality wood along with low-quality trees. Also, hardwood and thinning are included in the energy supplies. Biomass consisting of these four sources is harvested, gathered, dried to a standardized water content, chipped and transferred to the designated terminal site in the model created for financial assessment for forest fuel manufacturing in Anticosti island.

Variables that determine costs of forestry production, and thus also the production of forest fuels have been divided into three groups: Technology, biology and geography. Technology includes harvesting technology, in-forest transportation, drying (storage), chipping technology, and road transportation technology. Biology variable represents variation of trees that are harvested, their transportation and energy calculation. The last one, geography, includes site specific characteristics such as terrain layout, distance to terminal site, etc.

Forest fuel cost is determined by marginal costs, or the additional costs to traditional forestry. Marginal costs are calculated for each of the production stages (harvesting, collecting, drying, chipping and transportation). Variables (technology, biology and geography) influence the biomass sources processing (residues, low quality trees, hardwood and thinning), and thus influence marginal costs.

Price and availability are the final results that are calculated by this model (Table 9). Price of the forest wood is given in CAD/kWh, and the market price for the Anticosti island is about 0.11 CAD$.

Positive NPV is indication that the project is economically viable, the net value added of the project is 54,827,799$. The RETScreen model calculated the annual savings over the life of the Anticosti Island biomass which is 6,006,192 $. The financial analysis of the biomass cogeneration plant project shows that the project is profitable. After about 2 years we manage to recover the investment cost thanks to the income it generates, which reduces the risks since the return is fast, it is very important to minimize the risks. Total savings and annual incomes are 9,516,756 $, the annual fee is 4,375,033$ for an investment of 28,432,698$.