Coal-based generation capacity forms a significant proportion (over 60 per cent) of India’s total installed capacity. Hence, it is imperative for plant operators to adopt operations and maintenance (O&M) best practices to ensure efficiency in coal-based power plants and consistently meet the country’s growing energy requirements.
With time, the complexity of power plant operations has increased manyfold. Plants face myriad difficulties like rigorous demands from load despatch centres; frequent outages; prolonged periods of low load operations; improper ramp rates; and operations beyond design limits. These issues may increase in the near future due to the increasing penetration of highly intermittent renewable sources of energy. Plant operators must have a focused O&M strategy and should also target critical areas in order to maximise performance.
The following is an overview of some of the O&M best practices that can be adopted by coal-based thermal power plants (TPPs)…
These meetings can take place over one or two days. Their basic objectives are to review the operational performance of TPPs; identify major constraints and O&M problems; conduct a review of forced outages, partial loading details, measures for O&M cost reduction and optimisation, quality overhaul preparedness and the status of renovation and modernisation; as well as compile the statutory requirements along with safety practices.
The agenda and detailed discussion points of these operation review team meetings focus on issues pertaining to loss in plant load factors; loss in availability and partial loading; fuel linkage issues; ash utilisation; environment management; auxiliary power, special oil and make-up water consumption; and the parameters recording the best performance.
Occurrence analysis is introduced in the system as an enterprise process model. Its objective is to achieve operational excellence and zero forced outages.
At the outset of an occurrence, for example, if there is a tripping of equipment or a near miss, a first information report is generated from the station. This is then fed into an enterprise resource planning (ERP) system. In addition, other reports are generated for scrutinising and conducting expert analysis.
The inferences from this analysis are divided into three distinct categories: changes required in O&M practices; required design changes, if any; and corrective action and preventive action pertaining to design and engineering, erection and commissioning, O&M, condition assessment and competency building. Final recommendations are made on the basis of this analysis and the action points are addressed.
The implementation of the entire procedure in an ERP module can help in codification and, subsequently, in capturing repetitive failures.
This is a new practice that is currently being implemented only by a few utilities. With regard to asset health monitoring, the present practice involves the use of fixed and static alarm limits, which are monitored by unit control room engineers through distributed control system (DCS) input parameters. The fixed DCS alarm limit is independent of the equipment’s operating history, ambient conditions and maintenance statistics. It is based solely on equipment priority, making deviations in other parameters go unnoticed. There is no system for second-level monitoring unless a problem is flagged or is beyond the alarm limits. The absence of early warnings leads to the damage of equipment or components. Hence, there is a need to formulate dynamic threshold limits based on operating patterns.
This involves developing a series of operational profiles or patterns based on past behavioural analyses of equipment. These known operational profiles are compared with real-time data. The advanced pattern recognition (APR)-based system provides an alert much before the DCS alarm limit whenever the current operation deviates from the predicted one. APR is based on an algorithm of various parameters and is not confined to a single one.
APR-based systems provide advanced warnings of incipient failure modes and facilitate the continuous monitoring of the health and performance of equipment, helping experts provide advice on equipment performance and health scenarios. They also help in the identification of subtle changes in equipment behaviour and minimising operational risks.
Various types of maintenance practices can be deployed for optimising operations at thermal power stations. These include reactive maintenance, preventive maintenance, condition-based maintenance, predictive maintenance and reliability-centred maintenance (RCM).
Reactive maintenance forms the base of the maintenance practices pyramid and is also referred to as breakdown maintenance. It focuses on restoring equipment to normal operating conditions once equipment failure has already taken place. Preventive maintenance involves predetermined work that is performed as per a schedule with the aim of preventing wear and tear and sudden equipment failure. It helps protect assets, improves their useful life and system reliability, and also decreases the cost of system replacement and downtime.
Though Indian utilities had started with the adoption of preventive maintenance, they are currently deploying condition-based maintenance techniques. Condition-based maintenance attempts to determine equipment health by measuring parameters like vibrations, oil properties, electrical output, heat and sound. Data is acquired on these parameters, after which it is interpreted and corrective action is taken. This particular maintenance practice curtails surprise breakdowns, increases uptime, reduces the need for backups, optimises maintenance resources and leads to savings in maintenance costs.
However, there is immense scope for further increasing the efficiency of coal-based TPPs through RCM, which is the process of determining the most effective maintenance approach. RCM employs preventive maintenance, predictive maintenance, real-time monitoring, reactive maintenance and proactive maintenance techniques in an integrated manner to increase the probability of the functioning of a machine or equipment in a required manner over its design life cycle with minimum maintenance. The implementation of RCM by utilities enables them to increase equipment availability and reduce maintenance and resource costs.
Utilities should engage in advance outage management, which involves outage planning, scheduling, micro-scheduling and ordering spares and services. Such practices can assist them in the preparation of an outage readiness index, which is aimed at bringing about consistency in planning outages. The method identifies and defines the scope of the work needed prior to the commencement of an outage and quantifies the amount of preparedness required to implement it in the most cost-effective manner.
Technical audit of equipment and systems
Each component and system of a power plant has a certain level of efficiency. Regular technical audits can help in operating each of these components/ equipment/systems at their maximum efficiency levels.
Chemistry has often been ignored during the operation of TPPs. However, increases in unit size, and steam pressures and temperatures necessitate an evolved focus on chemical control. There is a need to apply superior grades of metallurgy to minimise or eliminate corrosion, deposits, cracks and equipment failures. Steps in this direction will help utilities increase cycle efficiency, enhance reliability, reduce forced outages, and enhance the focus on life cycle costs.
Around 50-60 per cent of power equipment failures take place due to the lack of O&M best practices. Hence, it is important to adopt the same and ensure that plant personnel strictly adhere to standard operating procedures. There is a further need to adopt a system-based approach, along with leveraging technology in the maintenance process to make it IT enabled. Moreover, there should be a focus on undertaking initiatives aimed at achieving zero forced outages and creating a centralised pool of experts. n
Based on a presentation by Kalyan Kumar Panda, Chief, Corporate Engineering, Tata Power, at a recent Power Line conference