3. An industrial process has an annual average electricity demand of 2.45 GWh/yr and a heat demand of 12,016.8 GJ/yr. The heat demand is currently served by a gas-fired boiler and electricity is purchased from the local utility. It is proposed to install a CHP (combined heat and power) unit, comprising a Stirling engine and a waste heat recovery (WHR) boiler. The anticipated operational hours are 6,205.5 hours-per-year. Data: Existing gas boiler LHV efficiency-75% CHP unit electrical output - 600 kW. Annual average CHP unit LHV electrical heat rate=12,166.5 kJ/kWh, CHP unit usable heat output = 3,222 MJ/h CHP unit availability - 90% Electricity tariff-37.5 /MWh Natural gas tariff -2.50 /GJ (LHV) Installed cost of CHP unit - 384,000 Maintenance cost of CHP unit-8.57 /kWh, b) Outline the design and operation of the proposed CHP system using ample schematics (including an energy balance diagram for the unit) to illustrate your answer. (15 marks) Draw a 'balance of energy demand' comparing the existing and proposed energy supply systems. Calculate the overall efficiency, the annual heat utilization, and the net annual savings of the CHP unit; hence determine the payback period required. Briefly comment on the results. (15 marks)