SCR Gas Temperature Control for Low Load Operation
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BOILER SERVICE SOLUTIONS SCR Gas Temperature Control for Low Load Operation Alstom has pioneered controlling SCR gas temperature for subcritical and supercritical steam cycles including drum-type and once-through boiler designs. Flexibility and Emissions Control Alstom offers advanced systems to control the gas temperature to the SCR so your plant can operate at low load and still comply with environmental restrictions. These systems are fully integrated with your boiler’s Control System (DCS) and are tailored to meet your plant’s demands. When the SCR gas inlet temperature approaches the minimum allowable range, the system is automatically engaged. At higher loads, they are inactive and do not impact the capacity or efficiency of the unit. Based on your unit’s design, Alstom can conduct an evaluation to determine maximum benefits for your plant’s low load operation. Subcritical Boiler: Alstom’s patented Hot Water Recirculation System (HWRS) controls the economizer outlet gas temperature (EOGT) by extracting a portion of the hot water from the boiler downcomers and mixing it with feedwater upstream of the economizer inlet. Supercritical Boiler: The patented Economizer Recirculation System (ERS) recirculates waterwall outlet fluid. These systems increase the fluid inlet temperature to the economizer, which increases the EOGT at reduced loads. Typical Economizer Outlet Gas Temperature with and without Alstom’s HWRS/ERS Typical Economizer Outlet Gas Temp. with Alstom's HWRS temperatures to SCR at loads as low as 35% • Alstom’s Systems have no impact on efficiency at higher loads • Only operates during required loads resulting in no parasitic power used at high loads • Increases boiler demand flexibility • Optimizes plant revenue Economizer Outlet Gas Temperature - F High SCR Limit High SCR Limit Operating Range of Operating Range with Alstom Recirculation Alstom Recirculation Gas Temperature Profile Gas Temperature Profile without Alstom Recirc. without Alstom Recirc. System System in Service Service Boiler Load - Percent © ALSTOM 2014. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited. Alstom contributes to the protection of the environment. This leaflet is printed on environmentally-friendly paper.

BOILER SERVICE SOLUTIONS SCR GAS TEMPERATURE CONTROL FOR LOW LOAD OPERATION ENVIRONMENTAL, OPERATIONAL AND ECONOMIC CHANGES Plant flexibility is key. Your plant’s boiler must be capable of turning down to a minimal load that matches grid requirements while meeting emissions standards and a low cost solid fuel. As boiler load is decreased, the inlet gas temperature to the SCR drops below the operating temperature window resulting in low load limitations for NOx removal. The Hot Water Recirculation System (HWRS) and Economizer Recirculation System (ERS) products are engineered and constructed...