Fuel Cell Systems Installation, Operation and Maintenance

Safety, Maintenance and Operability of Fuel Cell Plant Using Biofuels


Introduction

Some of the major concerns over the use of fuel cell plants, are the risks associated with the use of hydrogen gas. The following are some aspects of safety, maintenace and operability of fuel cell plants which the project team have considered.

The team have established a number of potential hazards to people and equipment, which can arise from operating a fuel cell plant. These are listed below - -

  • Explosion due to ignition of escaped biogas (CH4, H2S, CO, CO2) although most of the H2S will have been removed prior to introdution to a reformer.
  • Explosion due to ignition of escaped H2 gas
  • Failure of pressure containing equipment
  • Burns due to contact with high temperature surfaces or fluids, or frostbite due to contact with expelled gas expanding from high pressure.
  • Asphixiation if biogas, hydrogen or nitrogen gas (used for purging of the plant) build up in a confined space with human ocupancy.

    • Concepts and systems

    Sustainable energy

    CHP systems

    Biofuels

    Potential

    Applications

    Fuel Cells

    Gibbs energy

    Reformers

    Fuel cell performance

    Control and ancillaries

    Electricity and heat transfer

    Installation and operation

    Commercial availability

    Economics

    Environment

    Environmental aspects

    Index of technical reviews

    Risk Reduction and Control Measures

    Biogas

    Biogas will be supplied either to an external reformer for low temperature fuel cells or to internal reformers for high temperture fuel cells.

    Biogas must always be contained in appropriate pipes or storage vessels and precautions taken to ensure that leakage is prevented. Installations should be in accordance with Gas Safety (Installation and Use) Regulations 1984, relevant British Standards and Codes of Practice and Guidance Notes.

    In an enclosed area, appropriate gas detection equipment can be installed with alarm and emergency shutdown facilities. Continous gas monitoring is recommended. Such emergency shutdown systems should be hardwired and regarded as safety critical devices. If any leakge of biogas is suspected, isolate the biogas supply and extinguish all sources of of ignition. Non-flameproof electrical switches must not be turned on or off. In the event of of excesive leakage and a delay in isolating the supply, the affected building must be evacuated.

    If biogas from a pipe or valve is alight, isolate the supply promptly if it is safe to do so. If the supply cannot be isolated, do not extinguish the flame otherwise an explosive mixture of gas will be formed.


    Hydrogen Gas

    Hydrogen is extremely flammable with flammability limits of 4 - 75% v/v in air. Hydrogen can form explosive mixtures with air, oxygen and chlorine. If waste gas is to be ignited to part fuel a heat transfer or reforming process, due care and attention must be given to the design and operation of the burner/combustor assembly.

    When operating a fuel cell plant, the hydrogen gas should be used in enclosed systems. All equipment must be earthed to avoid static accumulation. Oils must never be used to lubricate the pressurised system.

    Hydrogen diffuses rapidly and may leak from a system gas tight for other gases. Any stored hydrogen must be kept away from any sources of ignition and must be segregated from all other compressed gases..

    The area in which the fuel cell plant is operated must be closely monitored for leakage of hydrogen gas. As for biogas, appropriate gas detection equipment can be installed with alarm and emergency shutdown facilities. Continous gas monitoring is recommended. Such emergency shutdown systems should be hardwired and regarded as safety critical devices.

    NOTE: Hydrogen gas burns with an invisible flame. In the event of fire, allow the gas to burn until the supply has been isloated then use an extinguisher appropriate to adjacent fires. Gas cylinders should be cooled with a water spray NOT a concentrated jet of water.


    Nitrogen Gas

    Nitrogen gas is required for purging of fuel cells and associated plant gas systems at shutdown and prior to strat-up, to remove the potential for a hyrogen or biogas (CH4) explosion. Although chemically inert for purging purposes, nitrogen gas is an asphixiant and care must be taken when handling it.


    Pressure

    If the fuel cell plant operates under presssure, appropriate pressure protection systems must be incorporated into the plant. Such devices can include pressure switches linked to hardwired trip protection, rupture discs or safety relief valves. Any relief must be to an area of low danger (ie to avoid explosion or asphixiation risks)


    Temperature

    If all or part of the fuel cell system operates at elevated temperatures, appropriate thermal insulation must be installed for personnel and equipment protection. Radiant heat can have a severe effect on the performance of instruments.


    Plant Life and Maintability

    Design life for fuel cell plants is based on the temperature of operatioin and catalyst life. At present, plant life figures from 14,000 to 40,000 hours are quoted. Systems operating at higher temperatures (SOFC and MCFC) have shorter lives.

    Maintainablity of the system could consider the folowing:

  • Calibration and function checks of safety critical systems
  • Ease of replacement of parts (is access straight forward?)
    The manufacturer or supplier should provide the following:
  • plant operating and maintenance instructions
  • commisioning spare parts
  • recommended spare parts list for 2 and 4 years if applicable
  • special tools if required




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