SUCCESSFUL IMPLEMENTATION OF METHANOL FIRING AT 50 MW GAS TURBINE FOR LONG TERM OPERATION

摘要

Recently methanol's use as a fuel is becoming more attractive. Firstly, because of the prices of NG (the main feedstock for methanol production) are now at record low. This has prompted consideration of other alternative energy sources that are not oil dependent. A second key issue has been growing global concern for environment and emphasis being placed on the use of fuels with lower SO_2, NOx and particulates emissions. Methanol offers these advantages, being a derivative of natural gas which partly de-linked from oil, and is a clean burning fuel. In this manner full scale test of methanol firing at FT4C TWIN PAC 50 MWe GT designed by Pratt & Whitney was performed. The obtained results clearly show that with minor low cost fuel system retrofit methanol firing leads to significant NOx, SO2 and particulates emission reduction. NOx emissions were reduced by more than 75% and are equal 75 mg/dNm3 at 15%O2. It is less then required standard even with water injection operation mode (the standard is 86 mg/dNm3 at 15%O2 of NOx emission). SO_2 emissions were reduced to zero with methanol firing. Particulate emissions vary from 1.3 to 1.6 mg/dNm3 at 15% O2 with methanol firing, while with LFO this parameter was 13-37 mg/dNm3 at 15% O2. However, it should be noted that methanol has a significantly lower calorific value, which is, for example, half of diesel oil and requires therefore some specific modification in gas turbine equipment. First, the existing fuel nozzles are too small for the higher volumetric methanol flow and should be replaced by high flow fuel nozzles. The existing fuel supplying pump should also be upgraded to the higher methanol flow. Modulating valve was also replaced due to the same reason. The paper first gives an overview of some of the key technical considerations of the gas turbine conversion from diesel oil to methanol firing, and results of long term operation of gas turbine fired by methanol. Based on the obtained results one may concluded that methanol is an attractive alternative fuel for meeting the energy needs of niche markets in an economic and environmentally sustainable manner, utilizing existing and/or new power generation units.