Quality Check

T&M solutions for emission control and power generation

Testing and measurement (T&M) solutions are adopted to enhance the operational efficiency of power pla­nts, lowering their emission levels and optimising their operations and maintenance. They also play a vital role in maintaining the life expectancy of power plant assets and are useful in early detection of failures, thus helping minimise equipme­nt outage. To this end, sensors and an­a­lysers are deployed to keep track of de­si­red plant parameters. These solutions help in maintaining efficient combustion by regulating the air-fuel mix and boiler conditions. Meanwhile, continuous emi­s­sion monitoring systems (CEMS) and predictive emission monitoring systems (PEMS) are gaining traction for their use in tracking emission levels and taking corrective measures.

Power Line takes a look at some of the T&M solutions that are being adopted by gencos to improve their efficiency…

Monitoring combustion

Efficient fuel combustion is essential for cost-effective power generation and em­ission reduction from power plants. Sufficient air is required to achieve complete coal combustion, while excessive air promotes NOx formation. Increasing the amount of air also lowers overall

pla­nt efficiency, as the increased volume of air flowing through the boiler leads to increased fan power consumption and greater heat losses. One of the solutions for maintaining the right air-fuel mix is monitoring the flue gas oxygen. The level of oxygen present in the combustion of waste gas is a key indicator of the amount of air supplied to the process. It can be monitored by using combustion gas oxygen analysers, which accurately measure the oxygen content in the combustion gas. Furthermore, these analysers can be used in conjunction with fl­ow meters to regulate the amount of air supplied to the burner. Actuators can also be used to operate the plant at the optimum ratio of fuel, air and operating pressure. Improving the range and accuracy of the sensor information available fr­om the boiler as well as using advan­ced control systems to maintain a balan­ce between boiler variables and optim­um input settings for any given situation is also useful.

Emission monitoring

CEMS: Gaseous components such as CO, NOx and SO2 need to be monitored continuously in the flue gas in the stack, along with gas flow, temperature and dust, to measure plant performance and emission levels. CEMS is a comprehensive solution for determining gas and/or dust concentration, accompanied by the required conversion to produce results in the units of the applicable emission limitation. The Central Pollution Control Board has mandated the installation of CEMS for real-time pollution monitoring of stack emissions, and a continuous effluent quality monitoring system in 17 categories of highly polluting industries, including power plants.

CEMS deploys complex extractive analysers, which remove flue gas samples from the duct and use a series of individual gas sensor modules or more advanc­ed spectroscopic techniques to determine the composition. Although stack measure­me­nts can be used in combustion control, it is preferable to analyse flue gas as close to the combustion pro­ce­ss as possible. Such in-situ analysis can take the form of sensors placed di­rectly in the flue gas, or line-of-sight optical absorption measurements, for which a transmitter and a receiver are placed on either side of the duct or furnace. CEMS provides continuous measurement of data on a real-time basis at the monitoring site of interest, even in the absence of skilled staff required to perform the analysis. In the sampling systems and online analysers, the corresponding major steps of traditional analysis such as sample collection, tra­nsportation, conditioning, calibration and analysis procedures are usually au­to­mated. In case of a sudden disturban­ce in the production process/pollution control system, the online analysers pro­vide timely information and, accordingly, im­mediate corrective/preventive mea­s­ures can be undertaken. Overall, CEMS can help gather real-time data, and allow plant operators to remotely access plant performance and conduct continuous per­formance checks of air pollution control devices/treatment methods.

In the adoption of CEMS, utilities face challenges in terms of choosing between different monitoring systems and multiple instruments, different suppliers and multiple data formats, multiple platforms and communication protocols, and data collection from heterogeneous systems. Going forward, there is a need to have coherence between central and state regulatory systems, clarity in the CEMS audit protocol, and a compliance mechanism. Further, there is a need to adopt the best available technologies for CEMS and hand-hold instrument suppliers and service partners, besides having a uniform display system irrespective of vendor or supplier.

PEMS: PEMS is a software-based solution that can provide reliable and accurate real-time emission estimations. PEMS uses an empirical model to predict emissions based on historical and real-time process data. PEMS exists as standalone versions, but is widely used as part of an integrated environmental mo­nitoring approach, capable of addre­ssing multiple sources in one plant. When combined with data acquisition and handling systems, and integrated in plantwide IT and communications networks, PEMS can be a viable diagnostic tool for lowering emissions and improving combustion efficiency through surveillance of emission variations and associated changes in plant process conditions.

Monitoring feedwater

To achieve optimum performance of a coal-fired power plant, careful monitoring of the quality of water and steam in the feedwater is essential. Multiple che­micals need to be monitored and controlled for optimum steam-raising efficiency. Dissolved oxygen in the feedwater can cause pitting in the boiler, reducing its operating life. Dosing the feedwater with hydrazine reduces oxygen to form nitrogen and water. How­ever, ex­cess hydrazine is wasteful and costly, whereas too little is unable to adequately control the dissolved oxygen levels. Further, pH analysers are used for monitoring feedwater acidity or alkalinity, and conductivity analysers are used to measure ionic content. As they indicate the level of contamination, they can be used to decide the type and duration of treatment required. They are also useful in minimising boiler erosion.

Other T&M instruments

Drones are being increasingly deployed to remotely monitor power plants as they can track changes in performance over time. The use of drones for inspection offers several advantages such as evaluation of the power plant condition, monitoring of inaccessible areas, re­duced plant downtime and mainten­ance costs, and safety of power plant personnel. Drones are also relevant for monitoring of power stations with flue gas desulphurisation (FGD) eq­uip­me­nt. Further, lining failure due to inadequate material quality or fa­ulty workmanship, or even localised da­ma­ge, can lead to im­m­ediate corrosion and, possibly, structural damage. During a unit outage, dro­n­es can be operated inside the chimney. They provide a compre­hen­sive, high resolution image of the in­ternal lining system. Based on the data collected by the drone, the technicians can evaluate the lining and prepare a full report on its condition and any possible problems.

Moreover, the correct combination of T&M equipment plays a vital role in checking the health of the critical power plant equipment. At present, online inspection and troubleshooting procedures play a critical role for utilities in reducing costs and downtime, and im­p­ro­ving efficiency. T&M instruments such as electrical flue gas analysers, thermal imagers, digital manifolds and digital gauges are being used for quick decision-making and troubleshooting. These ins­tru­ments are user-friendly and wireless as far as the sensor and display are concerned. They are also internet of things enabled, precise and accurate. Further, they offer online viewing of the process parameters, which is of tremendous use in effective monitoring of power plants.

Sensors and analysers are also being deployed to keep track of the desired plant parameters. The T&M sector will also see many changes in the coming years due to the path-breaking innovations in artificial intelligence and machine learning. Moreover, the central government’s target of 500 GW of renewable energy capacity by 2030 is expected to create significant demand in the coming years for the T&M of renewable energy equipment including solar cells, solar photovoltaic modules and wind turbine generators.

Conclusion

T&M solutions are vital for maintaining the operational efficiency of a power plant as well as lowering and maintaining emission levels. Further, they are useful for enhancing the life of power plant equipment, and in avoiding lapses in preventive and predictive mainte­na­n­ce that can lead to unsafe conditions, system breakdown, and revenue loss. Hen­­ce, adoption of comprehensive T&M solutions for power plants will go a long way in providing real-time data so that utilities can repair or replace faulty units in time.

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