SCR SYSTEMS WHAT YOU NEED TO KNOW

Transcription

1 SCR SYSTEMS WHAT YOU NEED TO KNOW Presented by: Ed Chan, Director Business Development Submitted: September 13, 2018 Creating a World of Possibilities

2 With more emphasis being placed on operations to reduce their environmental footprint, we are seeing increased demands of regulatory and performance standards. Advancements with Selective Catalytic Reduction (SCR) is proven to reduce these emissions, however not all SCR systems are the same. You need a system that will deliver for today and tomorrow, delivering optimal performance and efficiencies. So, here s what you need to know. AS NATURAL GAS IS CONSIDERED A CLEAN FOSSIL FUEL FOR ELECTRICITY GENERATION IS IT NECESSARY TO REMOVE POLLUTANTS? While natural gas is considerably cleaner than other fossil fuels and biomass solids, natural gas when combusted produces nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O) (the first two forming the mixture known as NOx). Unburned hydrocarbons (UHC, usually expressed as equivalent methane) and particulate matter (PM) are also produced but are negligible while natural gas is considered free from sulphur (SOx/SO2). (Add here Paris accourd etc.nox emissions are of particular concern due to their contribution to ground-level ozone formation and acid rain.

3 WHY IS NOX FORMED FROM A GAS TURBINE? Production of NOx in a gas turbine is primarily thermal and results from the reaction between oxygen and nitrogen from the air. In the combustion chamber of a gas turbine, fuel and compressed air are burnt at temperatures of over 1000 C and even up to 1600 C in the newest and largest turbines of 400 MW for 60 Hz and nearly 500 MW for 50 Hz. NOx emissions start forming in massive amounts when flame temperatures reach over 1450 C (2642 F). NOx production is highest at fuel-to-air combustion ratios of 5 7% (25 45% excess air), and depend on the type of turbine. Lower excess air levels starve the reaction for oxygen, and higher excess air levels drive down the flame temperature, slowing the rate of reaction. WILL HIGHER EFFICIENCY GAS TURBINES AND POWER PLANTS REDUCE THE AMOUNT OF NOX PRODUCED? With higher firing turbines now at over 1600 C (2912 F) and efficiency improvements such as supplemental duct-firing and waste heat recovery, improvements in turbine efficiencies can actually lead to higher, not lower, NOx production. As a rule of thumb, an increase in the combustion temperature by 50 C approximately doubles NOx emissions. HOW MUCH NOX DOES A GAS TURBINE PRODUCE? Turbines burning natural gas with no primary or front-end NOx control can have average hourly NOx emissions ranging from 100 to 300 parts per million (ppm) or higher (roughly 200 mg/nm3 600 mg/nm3 at 15% Oxygen (O2). On power plant sites with multiple turbines, NOx emissions can add up significantly up over the course of a year. WHAT DOES AN SCR DO? Selective catalytic reduction (SCR) converts nitrogen oxides with the aid of a catalyst into diatomic nitrogen (N2), and water (H2O). A gaseous reductant, typically anhydrous ammonia, aqueous ammonia or urea turned to ammonia, is added to a stream of exhaust gas with Nox and reacted over a catalyst. Primary reactions are: Secondary reactions are: 4 NH3 + 4 NO + O2 4 N2 + 6 H2O 8 NH3 + 6 NO2 7 N H2O 2 NH3 + SO3 + H2O (NH4)2(SO4) NH3 + SO3 + H2O NH4HSO4

4 The catalyst, comprised of parallel plates or honeycomb structures, is installed in the form of rectangular modules, downstream of the gas turbine in simple-cycle configurations. A SCR system is comprised of an ammonia storage tank, vaporization and injection equipment for ammonia, a SCR reactor with catalyst, instrumentation and control equipment, and tempering air system. WHEN IS SCR TECHNOLOGY USED? Many gas turbines currently only use primary techniques to reduce NOX emissions, such as Dry low-nox (DLN) and water injection. However, secondary techniques, such as SCR systems, have been necessary when regulations require very low NOx limits or DLN technology is unavailable or technically and economically prohibitive. In the US, NOx cannot exceed 2.5 ppm and, in some instances, 2.0 ppm in several states, such as California, Massachusetts and Connecticut. Several hundred SCRs have been applied in Austria, Japan, Italy, the Netherlands and the USA, with over two-thirds located in the latter country. CAN SCR BE USED IN OPEN (SIMPLE) CYCLE POWER PLANTS? Engineers of a major OEM publishing a paper on NOx removal for gas turbines in 2000 stated SCR cannot be used in simple cycle configurations, except possibly in lower exhaust temperatures. INNOVA Global s SCR and CO technologies were applied to simple cycle gas turbine units in the United States in the year following this statement. By July, 2002, INNOVA Global had SCR technology successfully installed on a total of 10 large simple cycle frame machines located in Utah and Arizona. Source: Schorr, Marvin M., Consulting Engineering and Chalfin, Joel, Manager, Environmental Engineering. Gas Turbine Nox Emissions Approaching Zero Is It Worth the Price? Schenectady, New York: General Electric Power Systems. Pg. 3. WHAT IS DIFFICULT ABOUT USING SCR DIRECTLY AFTER THE TURBINE EXHAUST? Simple cycle gas turbine exhaust temperatures range between C ( F) well above the maximum operating temperature of most conventional NOx reduction catalysts of C ( F). To lower exhaust temperatures to ensure the required chemical reactions, a tempering air system must be used. The tempering air system must not only draw in a precise amount of ambient air but must mix it quickly and uniformly with the turbine exhaust to drop overall exhaust temperature to the effective range of reaction temperatures all while preventing temperature spikes which can damage or over-cool the catalyst. Temperature variants can cause the catalyst to operate outside of the effective design activity point. This tempering air system requires additional design expertise which you can find on INNOVA Globas s website.

5 WHAT ABOUT AMMONIA SLIP? Ammonia is injected into the gas turbine exhaust stream via INNOVA s highly effective, patent-pending ammonia injection grid (AIG). The design of this AIG system for uniform ammonia distribution is critical. Ammonia molecules must find the fewer NOx molecules at uniform temperature and exhaust flow in order to react, and how precise is the amount of ammonia injected and how well it is mixed with the gas stream are two critical considerations. Excess ammonia that doesn t react with the NOx molecules, termed ammonia slip, is released via the exhaust stack and can be environmentally detrimental. INNOVA Global has developed a proprietary, patent-pending AIG and distribution system, that guarantees lower ammonia slip of 5 ppm along with high NOx reduction. WHAT IS THE BEST-AVAILABLE-TECHNOLOGY (BAT) / BEST-AVAILABLE-CONTROL-TECHNOLOGY (BACT) FOR OPEN CYCLE TURBINES. At a recent project in Massachusetts, INNOVA lowered NOx emissions by 96% to 2 15% O2. Special measures by INNOVA Global, including unique catalyst beds and sealing achieved this reduction in NOx levels. WHAT IS NEEDED TO CONTROL CARBON MONOXIDE (CO) An inverse relationship between the formation of NOx and CO exists. Higher combustion temperature and pressure levels are conducive to NOx formation but out of range of ideal CO forming conditions. If conditions within the gas turbine combustion chamber are lower temperature, NOx emissions come down, but CO and hydrocarbons can rise in the form of an incomplete burn. In conjunction with SCR for NOx reduction, an oxidation catalyst to concurrently meet BAT/BACT emission levels for CO is used. In catalytic oxidation, a catalyst is used to oxidize CO. The addition of a catalyst to the basic thermal oxidation process accelerates the rate of oxidation by adsorbing oxygen from the air stream and CO in the flue gas stream onto the catalyst surface to react to form carbon dioxide (CO2) and water. Typical control efficiencies from an oxidation catalyst are between 80 to 90%.

6 WHO DO YOU CHOSE THOSE THAT SAY IT CAN BE DONE OR THOSE WHO HAVE DONE IT For over a quarter of a century, INNOVA Braden has been a global leader in the supply of ancillary equipment for gas turbine applications. The combination of our SCR technology, coupled with international fabrication capabilities and exhaust structural design expertise, ensures efficient operations with optimal performance. EXPERIENCE MAKE THE DIFFERENCE We don t just talk about what can be done, we do it. Our expertise includes the design and supply of catalyst systems complimented by the experience of over one thousand exhaust systems including stacks and silencers. It s that direct experience that has made us global leaders delivering best-in-class solutions every time. 233 Successful Simple Cycle SCR Projects 205 SCRs Installed for GE Gas Turbines 11 SCRs Installed for Solar Gas Turbines 16 SCRs Installed for Siemens Gas Turbines Up To 96% NOx Removal Down To 2.0 PPM NOx Down To 5.0 PPM Ammonia Slip FOR MORE INFORMATION On our advanced SCR Technology and how INNOVA can assist you in meeting and surpassing increased demands of regulatory and performance standards, visit INNOVA-gl.com or contact: Ed Chan Director, Business Development INNOVA Braden Europe P. +31 (0) E. Ed.Can@INNOVA-gl.com

7 OTHER SOURCES OF INTEREST Lecomte, Thierry et al.(2017) Best Available Techniques (BAT) Reference Document for Large Combustion Plants. Industrial Emissions Directive 2010/75/EU. JRC Science for Policy Report, 2017: EUR Eng. Available at: Schorr, Marvin M., Consulting Engineering and Chalfin, Joel, Manager, Environmental Engineering. (2000). Gas Turbine Nox Emissions Approaching Zero Is It Worth the Price? Schenectady, New York: General Electric Power Systems. Available at: gas-turbine-nox-emissions-approaching-zero-worth-price.pdf. Kato, Stephanie et al. (2004). California Environmental Protection Agency, Air Resources Board, Stationary Source Division. Report to the Legislature: Gas-Fired Power Plant NOx Emission Controls and Related Environmental Impacts. State of California. Available at: Milieu Ltd., the Danish Environmental Research Instititute, and the Center for Clean Air Policy (2004). Case Study 2: Comparison of the EU and US Air Quality Standards & Planning Requirements. Available at: OECD. (2018). Best Available Techniques for Preventing and Controlling Industrial Pollution, Activity 2: Approaches to Establishing Best Available Techniques (BAT) Around the World. Paris, France: OECD, Environment, Health and Safety, Environment Directorate. Available at: Scheible, Mike, Deputy Executive Office, California Air Resources Board. (2006). California s Success in Controlling Large Industrial Sources. Available at: nescaum.org. California Air Emissions Board. (2014). Rule 2.34 Stationary Gas Turbines: Adopted July 13, 1994; Revised November 12, Oct. 24, 2014.

8 Creating a World of Possibilities INNOVA Global is a leading supplier of specialized and balanced solutions for air and noise emissions control, acoustic consulting and mitigation, gas turbine auxiliary systems, manufacturing and turnkey buildings. Backed by 40 years of ingenuity and a strong commitment to client excellence we deliver performance and efficiencies for our customers in the power generation, oil & gas, petrochemical, mining, transportation, processing, recycling and other industrial sectors. With offices strategically located throughout the world, we ensure global expertise combined with a local focus in everything we do. INNOVA-gl.com