Objective The overall objective of this project was to demonstrate the effectiveness of the METHANE de-NOX ® (MdN) Reburn process in the Forest Products Industry (FPI) to provide more efficient use of wood and sludge waste (biosolids) combustion for both energy generation and emissions reduction (specifically from nitrogen oxides (NO x )) and to promote the transfer of the technology to the wide range of wood waste-fired stoker boilers populating the FPI. This document, MdN Reburn Commercial

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... hnology Manual, was prepared to be a resource to promote technology transfer and commercialization activities of MdN in the industry and to assist potential users understand its application and installation requirements. The Manual includes a compilation of MdN commercial design data from four different stoker boiler designs that were baseline tested as part of the development effort. Design information in the Manual include boiler CFD model studies, process design protocols, engineering data sheets and commercial installation drawings. Each design package is unique and implemented in a manner to meet specific mill requirements. Technical Perspective Recovering energy from by-product fuels consisting of biomass, wood wastes and solid residues are important in operating a mill efficiently. Wood waste fuels are typically burned to generate steam in a stoker boiler for process or power production; these boilers are commonly referred as a hog fuel-fired stoker boiler. Combustion of waste fuels can be limited by their low and variable heating value, high moisture content and presence of fuel-bound nitrogen content, however. High moisture wood waste and solid residue fuels are difficult to burn and contribute to poor fuel distribution which results in inefficient combustion and increased emissions of carbon monoxide (CO) and NO x . Fuels with high nitrogen content such as secondary and tertiary treatment solids also contribute to increased NO x emissions, limiting the ability to fire these fuels in boilers operating near their NO x permit limit. Cofiring supplemental fuel Gas Technology Institute MdN Reburn Commercial Technology Manual iv such as natural gas through auxiliary burners helps to improve combustion effectiveness and reduce NO x emissions; however, these benefits are typically limited to the fractional input of the cofiring fuel. Technical Approach In 1988, a research team led by GTI developed a cost-effective NO x reduction process for solid fuel-fired stoker applications called METHANE de-NOX (MdN). MdN is a patented reburn technology for reduction of NO x emissions solely for stoker furnaces. In this process, a portion of flue gas is recirculated (FGR) and combined with natural gas for injection above the grate combustion zone. Injection of reburn fuel with FGR in the lower furnace provides an oxygen-deficient environment, greater turbulence and mixing, and higher, more uniform temperatures. Less-oxidizing conditions at the grate promote the decomposition of fuel-bound nitrogen compounds to reduce nitrogen oxide formation. Increased temperatures generated above grate also boost the effectiveness of grate combustion. Air distribution between the undergrate and overfire air is also adjusted to reduce oxygen availability in the lower furnace and improve burnout in the upper furnace. Successful commercial-scale demonstrations were conducted on municipal solid waste (MSW) operations and coal applications in the 1990s. Based on these past technology successes, DOE's Office of Industrial Technologies (OIT) through the Agenda 2020 initiative in 1997 provided support along with GRI, IGT, SMP and industrial partners in development efforts to adopt the MdN technology to applications in the FPI. Results Field-evaluations (commonly called baseline tests) were conducted at four (4) different hog fuel-fired stoker boilers at pulp and paper mills located in the U.S. (International Falls MN, DeRidder LA; Port Hudson, LA; and Wallula WA). These selected stoker boilers covered a variety of different stoker design configurations; grates consisted of water cooled-vibratory, traveling spreader, and water cooled-stationary pinhole types. Physical dimensions of the furnace ranged from square to rectangular and pneumatic spreader type fuel distributors was common to all systems. Each boiler was equipped to co-fire natural gas from dedicated burners and bark was the major fuel constituent for grate combustion. Other waste fuels fired included waste water treatment sludges and non-condensable gases, both high volume low concentration (HVLC) and low volume high concentration (LVHC) streams. Baseline Tests collected data about the boiler operation and chemical composition of in-furnace gases through sampling with special water-cooled probes. Analysis of this data provided the basis for: 1) determination of NO x formation zones in the furnace; 2) Gas Technology Institute MdN Reburn Commercial Technology Manual v assessment of boiler variables impact on NO x emissions and 3) estimation of benefits from an MdN Reburn retrofit. This development effort also included creation of a custom computational fluid dynamic (CFD) wood waste stoker boiler model using Fluent software, specifically to help in technology transfer, application, optimization and commercialization of the MdN process in the FPI. Demonstration of MdN technology in the FPI was first implemented at a mill located in International Falls, MN. Performance with MdN provided significant benefits such as a 300% increase in sludge combustion (savings in landfill volume and disposal costs); a 30% decrease in natural gas usage, a 40% reduction in NO x emissions, and an increase of about 1% in thermal efficiency. A second MdN boiler retrofit design was commercially installed and successfully commissioned on hog fuel-fired boiler at the Port Hudson, LA mill in 2001. At Port Hudson, a 30-40% reduction in NO x emission was achieved. Presently, both systems are in full-scale, continuous operation Furthermore, a technology licensing agreement with Energy Systems Associates-Environmental Solutions (EAS-ES) located in of Pittsburgh, PA to market and install MdN reburn technology was successfully negotiated. ESA-ES's staff of engineers is skilled in combustion, boiler operation and emission control technologies. Project Implications METHANE de-NOX Reburn process applied to wood waste-fired stoker boilers maximizes the use of hard-to burn industry byproducts such as wood waste solids, sludges and biomass through an effective use of natural gas to ease the cost of energy production and reduced emission of gaseous NO x in compliance with regulated environmental limits. The technology is cost-effective; relatively easy to retrofit and install. GTI Project Manager Stan Wohadlo Senior Engineer, Power Generation Gas Technology Institute MdN Reburn Commercial Technology Manual vi Executive Summary Pulp and paper companies comprise a highly energy-intensive industry in which production wastes such as bark, hog fuel and clarifier solids (sludge) are routinely used as fuel. Economic pressures are forcing pulping processes to utilize more of the wood fiber and the waste fuels available for steam and power generation. Recent enactment of EPA's cluster rules for the pulp and paper industry is resulting in more non-condensable gas (NCG) streams being generated and which require disposal in an economic and environmentally sound manner. Declining solid fuel quality and increasing combustion of waste gases is increasing dependence on expensive cofiring fuels like oil and natural gas to maintain combustion stability, steaming capacity and emissions limits in the industry's waste-fired boilers. Increasing prices for natural gas put a severe economic strain on the industry and underscore the need to develop more effective and economic combustion methods to recover energy from mill waste streams. METHANE de-NOX (MdN), a natural gas-based reburn technology developed by GTI in the 1990s and already successfully demonstrated in commercial demonstrations on stoker boilers for power generation using municipal solid waste and coal as fuels provides improved combustion performance, reduction in emissions (specifically NO x ), and increased thermal efficiency compared to conventional gas cofiring schemes. As a result of these process benefits, a development project was awarded in 1999 under a DOE Cooperative Agreement DE-FC36-99GO10418 to extend and demonstrate the technology in applications related to the Forest Products Industry (FPI), specifically on hog fuel-fired stoker boilers found in pulp and paper operations. Later, additional funds were granted to study use of NCGs generated in a pulp and paper mill as replacement for a portion of the reburn fuel used in a conventional MdN retrofit; further reducing natural gas consumption and saving costs. A major effort in the overall development activity included field evaluations of four (4) hog fuelfired stoker boilers at different pulp and paper mills located in the U.S., out of which then led to two (2) successful commercial-scale MdN installations, currently in continuous operation today. The first commercial-scale installation was for demonstration purposes on a bark and sludgefired stoker boiler rated at 200,000 lb/h MCR (maximum continuous rating) at Boise Cascade's mill in International Falls, MN. With MdN in operation, significant improvements in key boiler performance areas were achieved: • Reduced emissions of stack NO x by over 40%, equivalent to approximately 180 tons/boiler/yr with reburn natural gas injection at 9.5% of the boiler's thermal input • Increased grate sludge combustion by a factor of 3, which reduced mill's landfill volume and sludge disposal costs (a $396,000 reported savings per year) • Increased boiler thermal efficiency by 1 to 2% • Decreased unburned carbon in bottom and fly ash by 30% • Performance of MdN boiler retrofit at International Falls recognized by industry with a 1999 AF&PA Environmental and Energy Achievement Award Gas Technology Institute MdN Reburn Commercial Technology Manual vii The second MdN system was a commercial installation at a mill in Port Hudson LA where a 30-40% reduction in NO x emissions was achieved. In an effort to promote the technology and its commercialization to the variety of hog fuel stoker boiler designs operating in the FPI, GTI developed a custom CFD stoker boiler model to provide basic MdN boiler retrofit design support and a tool for process optimization studies. A licensing agreement was executed with Energy Systems Associates-Environmental Solutions located in Pittsburgh PA to market the technology in North America. And this document, MdN Reburn Commercial Technology Manual, was prepared to serve as a resource to potential users in understanding the application and installation requirements of the technology. Gas Technology Institute MdN Reburn Commercial Technology Manual