Ultra Low NOx Conventional and Regenerative Burner Retrofits

Paper from the AFRC 2015 conference titled Ultra Low NOx Conventional and Regenerative Burner Retrofits

The first section of the paper will focus on cold/hot air burner conversions to Ultra low NOx hot air burners. It will be illustrated that a cold air burner can often be retrofitted to an Ultra Low NOx hot air burner with minimal or no change in NOx emissions, despite the increase in air temperature. In addition, it may be possible to make changes to the burner internals only in order to make the conversion. The paper will illustrate retrofits from hot air to Ultra low NOx hot air burners. To make these changes, furnace manufacturers would require little or no modification to the furnace wall opening to accommodate the new burner.; The second section of the paper will focus on Regenerative burner conversions. Because regenerative burners are fired in pairs, the perception may be that twice as many burners are required to replace existing conventional burners. However, an increase in burner capacity, furnace circulation, and efficiency may allow the actual number of burners to even be reduced. Ultra low NOx regenerative retrofits are also possible using the latest Regenerative CyclopsTM technology. With the regenerative CyclopsTM Burner, NOx emissions are reduced by nearly a half as compared to market leading regenerative burners.

Bloom Engineering Company, Inc. Ultra Low NOx Conventional and Regenerative Burner Retrofits AFRC 2015 Dave Schalles - V.P Technical Services Matt Valancius - Manager - Marketing & Strategy Executive Summary One economical way to upgrade a furnace (for efficiency gains, NOx reduction, etc.) is to perform retrofits on existing burners. By retrofitting burners, it is often possible to see improved performance over the old burner at a reduced cost of a replacement burner. The first section of the paper will focus on cold/hot air burner conversions to Ultra low NOx hot air burners. A cold air burner can often be retrofitted to an Ultra Low NOx hot air burner with a reduction in NOx emissions, despite the increase in air temperature. In addition, it may be possible to change only the burner internals in order to make the conversion. The paper will also illustrate retrofits from hot air to Ultra Low NOx hot air burners. These changes often require furnace manufacturers to make few or no modifications to the furnace wall opening to accommodate the new burner. The second section of the paper will focus on Regenerative burner conversions. While conventional to regenerative retrofits generally require additional new equipment, the increases in combustion efficiency (and the resulting decrease in fuel usage) mean that such projects are viable options for furnace upgrades. Ultra Low NOx regenerative retrofits are also possible using the latest Regenerative CyclopsTM technology. With the Regenerative CyclopsTM Burner, NOx emissions are reduced by nearly a half as compared to market leading regenerative burners. Introduction Upgrading burners is often an effective way to achieve process improvements such as increasing productivity, decreasing fuel use, and/or minimizing NOx and CO2 formation. One of the most economical ways to perform an upgrade is by retrofitting an existing burner with new technology. Often, the modifications to the burner are comparatively minor, and sometimes simply require changes to the internal components without the need for External Flue Gas Recirculation (FGR) or Selective Catalytic Reduction (SCR). Presently, the steel industry is seeing low capacity utilization, so increased production is not a primary concern for retrofits. The aluminum industry, however, can definitely benefit from improved melt rates. The other major driver for burner upgrades, and thus retrofits, is the increasing importance of NOx and CO2 reduction. As regulations become more stringent, both the steel and aluminum industries will continue to require improved technology. Conventional Retrofits Both hot air and cold air burners can be good candidates for a retrofit. The most common way to upgrade a cold air burner is to do a conversion to hot air (usually with an accompanying reduction in NOx due to technology improvements). Hot air burner upgrades usually are simply for NOx reductions, many times achievable simply with modifications to the internal burner components. It is, of course, necessary to evaluate the entire combustion system (for flow, pressure, temperature, etc.) when making any kind of changes to the burners. COLD AIR TO HOT AIR ULTRA LOW NOX Design The primary benefit achievable from a cold air to hot air conversion is a reduction in fuel use by the increase in combustion efficiency. These kinds of conversions could require significant modifications to the burners (although modifications could also be very minor). Recent developments in retrofitting technology have generally minimized the amount of work required to modify the burners. Because combustion efficiency increases with combustion air preheat temperatures, the fuel input required for the same process requirements decreases (unless productivity increases are part of the upgrade as well), thus necessitating an evaluation of the whole combustion system. FIGURE 1: Sample Cold Air to Hot Air Ultra Low NOx Conversion Figure 1 illustrates a typical conversion from a cold air to a hot air Ultra Low NOx burner. Some modifications to the burner are required. Please reference Figure 1 and corresponding numbers: 1 - Refractory lining for the burner is required if the new air temperature exceeds the design temperature of the existing burner. 2 - The gas nozzle may need to be replaced for a few reasons. First, it would require replacement if the new Ultra Low NOx fuel nozzle requires higher pressure or a different spray angle/type. Second, the fuel nozzle length may need to be modified to accommodate changes to the air nozzle. The materials of construction of the fuel nozzle must also be evaluated for a higher combustion air temperature. 3 - The air nozzle/baffle would need to be replaced in ALL types of Ultra Low NOx conversions. Air/gas staging and air nozzle design is critical to minimizing peak flame temperatures and NOx emissions. 4 - The gas connection may also need to be relocated at the rear of the burner. Non-symmetrical combustion and gasstaging are two reasons why the connection location may need to be modified, thus requiring a new end plate. Bloom Engineering Company, Inc. 2 5 - In some cases the port diameter and port angle may require modification. Port Density (Btu/in2 [of the port area]) (the maximum amount of heat load/capacity in a given burner size and port diameter) of the design may be the limiting factor in potential conversion. 6 - Changes to the port may necessitate expansion of the opening in the furnace wall. Such expansions are more often required when air staging occurs in the port block itself - generally in smaller capacity burners. 7 - In some cases, a completely new burner body may also be required depending on the requirements of the internal burner design and existing burner configuration. PERFORMANCE Table 1 summarizes the expected emissions for both a cold air burner and hot air Ultra Low NOx burner with an expected reduction in emissions shown in both a lb/MMBtu and lb/hr basis. Because the required installed capacity for a hot air system is less than a cold air system (for the same Available Heat requirement), there is a more significant benefit on a lb/hr basis. Cold Air Hot Air Ultra Low NOx Available Heat 20 20 MMBtu/hr Air Preheat 100 800 °F 51.10% Thermal Efficiency 37.40% HHV Installed Capacity 53 39 MMBtu/hr Expected NOx Average 0.138 0.044 lb/MMBtu Expected NOx Rate 7.4 1.7 lb/hr Expected CO2 Average 118 118 lb/MMBtu Expected CO2 Rate 6,310 4,618 lb/hr Annual Hours 8760 8760 hours Expected NOx PTE 32.3 7.5 tons/year Expected CO2 PTE 27,639 20,229 tons/year Table 1: Expected NOx and CO2 of Cold Air and Hot Air Ultra Low NOx burners Assumptions: 2200 °F POC Temperature, Natural Gas fuel, 10% Excess air Case Study The following case study in the Aluminum industry required the conversion of cold air burners to Ultra Low NOx burners in three unique applications. Best available burner technology was utilized to meet the strict requirements. Requirements: • Aluminum Melter, Holder, (2) Homogenizers • Ultra Low NOx requirement in California Challenges: • Ultra Low NOx required at all operating points • Emissions guarantee mandated the use of incremental primary air control as furnace temperature increased Design: • Ultra Low NOx hot air burners with internal flapper valve for Melter • Small Capacity Ultra Low NOx burners for Homogenizer and Holder Bloom Engineering Company, Inc. 3 • Field tuned to maximize flame signal and NOx reductions at all operating points Results: • Technology delivered BACT (Best Available Control Technology) NOx and exceeded customer expectations in all cases • Public Permit Limit NOx not to exceed 37 ppmvd@3%O2 (RECLAIM Concentration Limit) in California SCAQMD agency. The low NOx burner is considered achieved in practice. HOT AIR TO HOT AIR ULTRA LOW NOX This type of conversion is most often implemented for reduction in emissions only. Burners may also be retrofitted as part of an overall upgrade to the furnace. DESIGN Design parameters for converting from a hot air to a hot air Ultra Low NOx burner are similar to a cold air conversion in many aspects. If the required fuel input remains unchanged, minimal changes are necessary for the combustion system. FIGURE 2: Sample Hot Air to Hot Air Ultra Low NOx Conversion 1 - If the burner is already designed for hot air, no change to the burner lining is typically required 2-7 - See comments above for Cold to Hot Air Ultra Low NOx expansion PERFORMANCE Table 2 shows expected emissions performance which varies depending on the required emissions levels and installation requirement/restrictions. Bloom Engineering Company, Inc. 4 Hot Air Hot Air Ultra Low NOx Available Heat 20 20 MMBtu/hr Air Preheat 800 800 °F 51.10% Thermal Efficiency 51.10% HHV Installed Capacity 39 39 MMBtu/hr Expected NOx Average 0.337 0.044 lb/MMBtu Expected NOx Rate 13.2 1.7 lb/hr Expected CO2 Average 118 118 lb/MMBtu Expected CO2 Rate 4,618 4,618 lb/hr Annual Hours 8760 8760 hours Expected NOx PTE 57.8 7.5 tons/year Expected CO2 PTE 20,229 20,229 tons/year Table 2: Expected NOx and CO2 of Hot Air and Hot Air Ultra Low NOx burners Assumptions: 2200 °F POC Temperature, Natural Gas fuel, 10% Excess air CASE STUDY The following case study reviews the conversion of hot air burners to a hot air Ultra Low NOx design. The steel facility was required to reduce plant-wide NOx emissions significantly. The 80" Hot Strip Mill was a primary candidate at the plant for implementing NOx reduction technology because it was a high fuel use application and there was a potential to reduce emissions drastically at minimal cost. Requirements: • Steel Rolling Mill • Reduce NOx emissions at hot strip mill • 4 Furnaces total • Approximately 200 tph per furnace Challenges: • Customer did not have money in budget to replace existing walls • no changes to combustion air piping were allowed • conversion of only approximately 80% of current installed capacity • Natural gas and Coke Oven Gas (60% Hydrogen) design requirements with fuel pressure limitations (available at less than 2 psig) Design: • Modified design 2-1/2 times the port density (Btu/in2) to fit new burners in existing wall openings Results: • NOx was 1/2 the level guaranteed • Burner/port requirements met • Slab quality improved • Burner internals proved durable • Public permitted NOx of 0.150 lb/MMBtu using Coke Oven Gas Fuel (includes fuel bound nitrogen (FBN)) with only ~80% of total burner capacity being retrofitted Bloom Engineering Company, Inc. 5 For this project, the customer mandated that the new Ultra Low NOx burners would fit within the existing port opening. Port Density is defined as burner capacity divided by open area of the port/tile, typically measured in Btu/in 2. Each unique burner is typically designed and scaled based on a specific port density. The requirement to match existing port diameters resulted in an Ultra Low NOx burner with a port density 2-1/2 times standard design parameters. The burner internals were redesigned to meet the new requirement, were lab tested, and were verified using CFD (Figure 3). The result led to a significant reduction in NOx while improving slab quality with a uniform furnace temperature profile. FIGURE 3: CFD Study showing existing and new burners operating at similar average zone temperatures Regenerative Retrofits The most significant production and fuel savings benefits can be gained through converting existing direct fired burners to regenerative burners. With developments in regenerative technology, in many cases, NOx emissions can also be reduced despite the increase in the combustion air temperature. CONVENTIONAL TO REGENERATIVE ULTRA LOW NOX When comparing to a cold air system, a regenerative system reduces air and gas line/equipment sizes while requiring the addition of the complete exhaust system. Flue system restrictions often limit burner capacity increases - regenerative systems can often provide an efficient solution to this problem. If a cold air system is being considered for retrofit to regenerative, approximately 90% of the air and gas equipment may be re-useable provided it is in acceptable condition. Additional cycle valves are required for air, gas, and exhaust. Cooling air equipment, start-up air equipment, and exhaust equipment (including an exhaust blower) are also required. DESIGN Modifying a furnace from a conventional system to a regenerative system provides significant thermal and/or production enhancements. Because of extremely high air preheat temperatures and regenerative devices that are required for each burner, existing direct fired burners cannot be reused. Space constraints must also be analyzed to accommodate the addition of a regenerative media box. Options such as a roof-mounted media case and dual head regenerative burners are sometimes needed for successful installations (Figure 4). PERFORMANCE Bloom Engineering Company, Inc. Figure 4-Dual Head Regenerative Burner 6 Despite a significant increase in air preheat temperature and thermal efficiency, expected NOx emissions on a lb/MMBtu and lb/hr basis can be improved, as shown in Table 3. Cold Air Hot Air Regenerative Ultra Low NOx Available Heat 20 20 20 MMBtu/hr Air Preheat 100 800 regenerative °F 72.60% Thermal Efficiency 37.40% 51.10% HHV Installed Capacity 53 39 28 MMBtu/hr Expected NOx Average 0.138 0.337 0.054 lb/MMBtu Expected NOx Rate 7.4 13.2 1.5 lb/hr Expected CO2 Average 118 118 118 lb/MMBtu Expected CO2 Rate 6,310 4,618 3,251 lb/hr Annual Hours 8760 8760 8760 hours Expected NOx PTE 32.3 57.8 6.5 tons/year Expected CO2 PTE 27,639 20,229 14,238 tons/year Table 3: Expected NOx and CO2 of Cold Air, Hot Air, and Regenerative Ultra Low NOx Burners Assumptions: 2200 °F POC Temperature, Natural Gas fuel, 10% Excess air CASE STUDY Sidewell charged continuous-type aluminum melters represent an excellent application of regenerative burners in the aluminum industry. The Ultra Low NOX regenerative burners can be justified for all new sidewell-charged aluminum melters. Retrofits will be economically justified in nearly all cases on these furnaces, due to the dramatic efficiency advantage for regenerative systems on continuous high temperature processes. The following case study on a Side-Well Melting Furnace demonstrates the capability to retrofit regenerative burners on a furnace designed originally for cold combustion air operation with inherent space limitations. Requirements: • Side-well Melting Furnace • Increase Melt Rate and Fuel Savings Challenges: • Long and narrow bath area • Existing flue location made it impossible for burner heads to straddle the flue • Space Limitations Design: • Dual Head Burner Design Results: • Customer expectations Met • Predicted production increase of 5,612 tons/year, $400,000/year fuel savings, and 1.1 ton/year NOx Reduction The solution was to provide dual head regenerative burners (1 regenerative media box + 2 burner heads). This provided superior bath coverage and short flame length than a standard burner with identical input (Figure 5). Bloom Engineering Company, Inc. 7 "A" Burners Firing "B" Burners Firing FIGURE 5: Dual Head Regenerative System REGENERATIVE TO REGENERATIVE ULTRA LOX NOX Regenerative technology has improved significantly over the years with respect to improved process control, reliability, maintenance, and emissions reductions. Slight improvements on thermal efficiencies across regenerative technologies may be possible, but would rarely be considered the primary reason for conversion. Design Because design principles are similar between regenerative technologies, upgrading technology may be limited to modifying burner internals requiring only minor alterations to the combustion system. PERFORMANCE Regenerative Regenerative Ultra Low NOx Available Heat 20 20 MMBtu/hr Air Preheat regenerative regenerative °F 72.60% Thermal Efficiency 72.60% HHV Installed Capacity 28 28 MMBtu/hr Expected NOx Average 0.1 - 0.3 0.054 lb/MMBtu Expected NOx Rate 2.8 - 8.3 1.5 lb/hr Expected CO2 Average 118 118 lb/MMBtu Expected CO2 Rate 3,251 3,251 lb/hr Annual Hours 8760 8760 hours Expected NOx PTE 12.1 - 36.2 6.5 tons/year Expected CO2 PTE 14,238 14,238 tons/year Table 4: Expected NOx and CO2 of Standard Regenerative and Regenerative Ultra Low NOx Burners Assumptions: 2200 °F POC Temperature, Natural Gas fuel, 10% Excess air Bloom Engineering Company, Inc. 8 CASE STUDY The following case study required production capacity improvements with minimal effects on NOx emissions on a Pusher Steel Reheat Furnace. Existing regenerative burners were converted to the latest regenerative technology. In addition, the soak zone of the furnace was extended and new longitudinally fired regenerative burners were added. Requirements: • Pusher Reheat Furnace (Midwestern Steel Bar Mil) • NOx guarantee • Increase capacity from 90tph to 125tph • Combustion System Reliability Enhancement Challenges: • Furnace rebuild with existing equipment Design: • Soak zone extended • Regenerative burners modified in other zones Results: • Achieved 10% below guaranteed NOx figures • Achieved 130 tph Production • Combustion system reliability improved • Approximately 1/3 the cost of a new furnace REGENERATIVE TO NEXT-GENERATION REGENERATIVE ULTRA LOW NOX DESIGN The 11650 Regenerative CyclopsTM utilizes non-symmetrical combustion in order to delay the mixing of the fuel and air for reduced NOx. A separate low velocity gas nozzle is used for cold start operation. The innovative burner design is available for retrofitting of existing regenerative burners. Performance The next generation of regenerative burners provides extremely low NOx emissions, very high efficiency, and increased production on existing furnaces. In Steel Reheat furnaces, in addition to NOx + CO2 reduction, the 1650 burner provides a production boost as compared to conventional systems. In Direct Charge and Sidewell Charged Melters, the 1650 burners provide 20 - 50% fuels savings vs. non-regenerative systems. These burners can also be applied to Forge Furnaces (Batch; In-and-Out), with similar fuels savings and NOx reduction as in an Aluminum Melter. NOx emissions are reduced by nearly a half as compared to Bloom's 1150 Series Regenerative Burner (Figure 6). 1 1650: PATENT PENDING-APPLICATION NO. 61/881,163; International Publication Number WO 2015/042237 A1 Bloom Engineering Company, Inc. 9 FIGURE 6: Relative NOx between leading regenerative technologies Conclusion Retrofitting existing combustion equipment can be a very cost-effective way to enhance production, save fuel, and reduce emissions. Advancements in burner and retrofitting technology have paved the way for improvement projects in a variety of applications and existing furnace/burner configurations. Bloom Engineering Company, Inc. 10