This paper presents a model of a combined heat and power (CHP) system, also known as cogeneration, for the purpose of analyzing the relationships between electricity generation, steam production, and fuel requirements for the steam assisted gravity drainage process (SAGD) used in bitumen production. The paper provides illustrative examples of assessments of the economics of the CHP process for alternate cogeneration arrangements and input assumptions.
The combined heat and power model (CHPM) simulates the operation of a gas turbine - electric generation system with the hot exhaust gases from the turbine being directed to a boiler for steam production for use in SAGD production operations. Alternately, a topping steam turbine - electric generation system with exhaust steam used in SAGD operations is simulated. The model provides estimates of the fuel requirements and electricity generated by the combined process. Illustrative examples of the application of the model provided in the paper include the use of alternate fuels, natural gas and petroleum coke, for the combined production of electricity and bitumen.
Bitumen mining and in situ extraction operations of Alberta are large users of natural gas and are projected to grow substantially over the next decade. However, since the turn of the century, the North American natural gas supply-demand balance has tightened and consequently gas market prices have risen substantially. Consequently, the Canadian Energy Research Institute (CERI) is examining alternate systems and fuels to reduce the cost of steam production for these operations.
The Combined Heat and Power Model (CHPM) described in this paper was developed specifically for the economic assessment of combined heat and power (CHP) systems for bitumen extraction by the steam assisted gravity drainage (SAGD) process. It calculates the fuel requirements and electricity generation rates for SAGD operations, which are required for an economic assessment of the operations. The economic analysis is performed in a separate model, the SAGD Supply Cost Model (SSCM), which calculates the supply cost of the extracted bitumen.
The CHPM simulates the operation of the steam plant of a SAGD operation, both with and without electricity generation. Gas and steam turbine options for the generation of electricity are included (See Figures 1 and 2 respectively). As shown in the figures, mass and heat energy flows of the system are outputs of the model. The principles of conservation of energy and mass are used for the calculation of the flows.
For the gas turbine option, Figure 1 shows that natural gas fuel is burned in a gas turbine to produce electricity. Waste heat in the exhaust gases from the turbine is recovered in a boiler, which produces steam for the bitumen extraction process. There is a steam-water separator, which produces 100% quality steam for the extraction process. Water from the separator is returned to the boiler. There is a process unit for the treatment of feed water and an option to return hot water produced by the bitumen extraction operations to this unit for recovery of heat in this stream.
