96/04203 Comparative analysis of the factors affecting small and medium scale gas turbine cogeneration in Australia and the UK

Abstract

The viability of gas turbine cogeneration in Australia is affected by technical, economic and 'cultural' factors. A combination of these factors must explain why in Australia, and in New South Wales (NSW) in particular, cogeneration is not as widely used as it is in some other countries. A model has been developed to analyse the economics of retrofitting gas turbine cogeneration to industrial sites with electrical loads in the range 3 to 30 MW, and with a wide range of heat loads. The model compares the cost of operating the cogeneration plant with the cost of generating steam in gas or coal-fired package boilers and purchasing power from the local supply authority. Supplementary firing of the turbine exhaust gases to increase the inlet temperature to the heat recovery steam generator is considered. This performance modelling of gas turbines is based on analysis of a large number of modern industrial and aeroderivative machines. For particular heat and power load details a range of gas turbines and heat recovery steam generators is trialled. The model calculates the simple payback period achievable with each combination. This model provides a quick estimate of the feasibility of cogeneration in meeting various heat and power loads. The output from the model for a set of typical NSW input data demonstrates that there is a wide range of possible solutions. For a 8 MW e (electrical demand) project paybacks range from less than 3 1/2 years to more than 10, depending on the buyback arrangements and the choice of machine size. Typical data from the UK result in generally shorter payback periods : cogeneration projects in NSW in the size range of interest are not normally able to achieve payback periods as short as similar sized projects in the UK. In order to assess the relative importance of the technical/economic and 'cultural' factors, a comparison has been made between the best paybacks achievable for various load combinations with input data from Australia and the UK. Based on the results of this comparison and the previous modelling work, it is concluded that if cogeneration capacity in NSW is to increase significantly, there must either be a fall in the price of natural gas relative to electricity, or Australian governments will have to enact policies in favour of the smaller cogenerator.