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O&M ISSUES

Operation and Maintenance of Cogeneration Plants

T he 24-MW cogeneration plant of Godavari Sugar Mills at Sameerwadi, Dist. Bagalkot, Karnataka is the most modern plant installed in the sugar sector by Desein Private Ltd. as Owner Consultant. Desein was awarded the Operation & Maintenance (O&M) activity of the plant to be carried out by their expert team of engineers, technicians and associated staff. The plant's instrumentation and control system Desein Distributed Control Management Information System (DDCMIS) is designed to control and monitor the process parameters to ensure smooth, safe and reliable plant operation. Normal control/supervision of the boiler function, steam turbine generator and other plant auxiliaries are carried out through the DDCMIS. Off-site packages such as the bagasse handling system, Demineralizer (DM) and ash handling plants are provided with independent Programmable Logical Controller (PLC) systems and are connected to the DDCMIS via a serial communication network.

The operation of a sugar mill cogeneration plant is entirely different from a captive power plant operated on coal or oil as fuel. Maintaining and controlling fire in the furnace is easier with such fuels, while in bagasse-fired boilers maintaining uniform fire depends on continuous regulation of bagasse to the furnace through its feeding system. Feeding of excess bagasse to its feed system beyond the firing rate may result in choking of chutes/feeders resulting in loss of fire and tripping of the plant at low temperatures. Operation of the plant through milled bagasse during the crushing season, and through purchased bagasse during the off-season has its own operating problems, which may result in choking of chutes and jamming of the furnace stoker and hence should be carefully looked into. In a nutshell, the smooth operation of a sugar cogeneration plant is entirely dependent on proper operation of the bagasse handling system.

O&M Elements

Administrative Control
 For proper administration, labor should be properly selected with experience in the same type of plant. Shift routines are to be planned considering leave schedules.

Liaison with plant owner regarding requirement and supply of process steam for the sugar plant, generation, availability, plant shut down for various maintenance/overhaul activities. A good operator studies the requirement trend and plans changes in the operating procedure and maintenance schedule to ensure good operation and availability of equipment. It is necessary to keep a close track of efficiency of the generating facility and organize corrective measures whenever required. Regular review of spare stock versus the requirement on the basis of planned shutdown and lead time to be made is required. Spares should be properly preserved during storage. A Master Library with drawings, O&M and spare parts manuals, plant commissioning and performance reports should be set up for effective operation and maintenance.

For Administrative Control, a logging practice should be followed, some of which are given below:-

  • Attendance Register/Identity Cards: To record daily attendance, and casual, sick and earned leave availed by employees.
  • Operation Status Log Sheets covering
    • Daily units generated
    • Daily bagasse consumed
    • Total power generation
    • Total Auxiliary Power Consumption of the cogeneration plant
  • Bagasse Inventory Data Sheets
  • Occurrence Report - occurrence in any system resulting in loss of power generation
  • Relay Setting Forms
  • Accident Report Form
  • Safety Manuals
A small reference book which will list Safety Practices should be followed for safe isolation of mechanical and electrical equipment including high voltage, safety rules, instructions, First Aid in case of accident, rules of fire fighting and disaster management, etc.

Operation Control
Under Operation Control there should be regular walk-around inspections and visual condition/monitoring of each equipment in operation and operating parameters should be recorded on the log sheets. Each starting operation and shut-down should be recorded in the station log book and "Occurrence Reports" for any unforeseen tripping and shut down should be prepared. Safe isolation of equipment being released for repair/servicing by the maintenance department should be carried out. Safety tags as per safety instructions and issue "Release Permits" should be installed.

Proper interaction is needed with transmission authorities for Load Dispatch and maintenance department and revise setting of protection relays to match with changes in fault levels as and when necessary.

For Operation Control, a logging practice should be followed, some of which are given below :-

  • Shift In-charge Log Book: For entry of General Conditions and comments by shift in-charge engineer during his shift
  • Operator's Log Book: To record entire operation of SG/TG, general defects, equipment released for maintenance, etc. during his shift. Similar log book to be maintained for other auxiliaries.
  • Switchyard Log Book: To record switching carried out and other communication concerning load dispatch
  • Bagasse Area Log Book: To record arrival of bagasse, operation of bagasse handling system release of any equipment for maintenance and other communication.
  • Equipment Release Register: To record date and time of release of equipment, list of isolating and safety tagging points, person to whom released and time and date of release of equipment back in operation.
  • STG Set Log Sheet: To record hourly parameters of various mechanical instruments and electric meters of SG and TG. One log sheet for each day of operation to be maintained.
  • Switchyard Log Sheet: To record reading on hourly basis of various indicating instruments and energy meters of each MV switchgear and 110 kV line.
  • Fuel Yard Log Sheet: To record daily log of contents and one sheet per day of operation to be generated
  • Defects Reporting Forms: One form for each type of defect during shifts and at the night shift will be sent to the maintenance department for necessary action.

Maintenance Control
For maintenance control, daily preventive maintenance activities as per schedule and immediate action in case of trouble shooting, and attending mechanical and electrical faults should be carried out.

For effective maintenance, a computerized system of preventive maintenance based on recommendations by the manufacturer, site conditions and past experience with similar equipment should be prepared. This system should schedule each maintenance activity, list out probable spares and consumable and manpower requirements, etc.

Protection relays, gauges, energy meters are to be regularly calibrated within expiry date. To minimize downtime, record of quality of oil of distribution transformer and other HV/MV transformers are kept so that filtration activities are planned along with plant maintenance.

For Maintenance Control, a logging practice should be followed, some of which are given below:-

  • Annual Maintenance/Overhaul Schedule: This should be followed for power stations for individual equipment.
  • Inspection Schedule: To follow the annual plan for inspection of individual equipment as per local regulations and statutory requirement from insurance companies.
  • Cardex for Equipment: A cardex for each piece of plant should be maintained. This should include brief specification, serial number, manufacturer information, inventory number, where installed; a list of daily/weekly/monthly/bi-annual/annual checks, when last carried out, when next planned, etc.
  • Cardex for Spares: A cardex for each type of spares in inventory to be maintained which should have reference to the manufacturer part number, specification, quantity required, lead time, etc.
  • Cardex for Protection Relays: A card for each electrical protection relay to be maintained which will have a serial number, specification, where installed, last date of calibration and testing, due date for next, and brief history of any problem/malfunction
  • Cardex for Energy Meters: A card for each energy meter similar to protection relays should be made. This should also have calibration curve of these meters attached with the card.

Last, but not the least, plant and equipment need to be regularly dusted and painted with epoxy paint for its longevity to minimize the corrosion effect of bagasse since flying bagasse is a great nuisance, which deposits on plant and equipment.

Courtesy: Mr S N Mehra, Vice President Desein India Group, Desein House, Greater Kailash II Adjacent to Savitri Complex, New Delhi 110048 Ph: 011-645 3761-65, 6220364, Fax: 011 - 623 8393