CATALYTIC DETECTION OF FUEL LEAKS IN GAS TURBINE UNITS: 2. Gas Fuels containing hydrogen, carbon monoxide and inert

摘要

The detection of explosive gas and vapors is a critical safety function in Gas Turbines (GT) units. On one hand, this subject is being revisited by the GT community and safety organizations with a main focus on conventional gas fired power units. On the other hand one sees currently an increasing use of alternative primary energies for GT units including both gaseous and liquid fuels such as LPG, naphtha, syngas and a wide series of low and medium BTU gas fuels. This has prompted GE Energy to undertake a comprehensive evaluation of commercial catalytic detectors that are of common use in the detection of gas leaks. In particular, the multiple announcements of coal-based project (IGCC) represented a strong motivation to launch this program that ambitioned to cover both hydrocarbon and non-hydrocarbon fuels, i.e. the largest CnHm/CO/ H_2/ N_2(CO_2) spectrum. This evaluation program has been jointly devised with and performed by the laboratory of INERIS, a French Institute devoted to safety and environment. Particular emphasis has been placed on the capability to detect combustible species at levels as low as 5% LEL (Lower Explosion Limit) that result from recent safety codes. The overall program has been break down into two parts. The response of catalytic detectors to hydrocarbon gas leaks (natural gases and naphtha vapors) has been addressed in 2004 and the corresponding results have been already published (ASME paper 2005GT68875). This first work phase has shown a satisfactory response of selected catalytic bead sensors towards the hydrocarbon paraffin series up to C8. The second phase (2005) tackled the detection of CH_4/CO/ H_2/N_2(CO_2) mixtures. In the authors' knowledge, there was a lack of data in the current literature as to the performances of catalytic detection for this specific class of fuels. A wide range of mixtures was tested to cover the extensive spectrum of medium and low BTU gas fuels, including: "weak natural gas", coal derived process gas (coke oven, blast furnace gas; COREX gas; etc.) and syngas. CO2 and N2 were used as inert components in concentrations from 20 to 80 % vol. This paper summarizes the results of this second evaluation phase. A satisfactory response to the different CH_4/CO/ H_2/N_2(CO_2) mixtures has been obtained in terms of sensitivity, accuracy and detection limits which satisfies the requirements of current codes and standards. The overall program confirms the possibility to use catalytic bead sensors as a single detection technology for covering virtually all the gas turbine applications. This includes, apart from natural gas: LPG, light distillates (naphtha; gas condensates and NGL), "weak" natural gas, Medium & Low BTU fuels (Coke Oven; Blast Furnace), hydrogen-rich fuels (refinery) and the syngas segments with however the notable exclusion of middle distillates (gasoil, kerosene).