Furnace Study Arcelor Mittal Monlevade, Combustol … Furnace Study.pdfFurnace Study . Arcelor...

TO:

FOR:

Furnace Study Arcelor Mittal Monlevade, Combustol built Billet

Reheat Furnace

Date: July 17, 2012

Bloom Brazil Order Number: BBO-2012-153

Gerdau Purchase Order Number: 20110184 dated December 22, 2011

From: Carlos Silva, Dave Toocheck & Steve O’Connor Phone: 0xx 11 8111-1304, 412 760 8721, 412 760 8741

Email(s): [email protected] ; [email protected]; [email protected]

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mailto:[email protected]



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected]

July 17, 2012 ArcelorMittal Av. Getuillo Vargas, 100 Centro Industrial 3593-395 Joao Monlevade – MG - Brazil Attention: Mr. Carlos Henrique Silveira Aguiar Subject: Furnace study of Combustol built slab reheat furnace Bloom Brazil Order No.: BBO-2100-153 Gerdau Purchase Order No.: PO 20110184 December 22nd, 2011 Dear Carlos: Thank you for the opportunity to assist you with improving the operation and efficiency of your reheat furnace. We feel that we have done a fairly thorough job in our analysis based on the data that we collected during our observations of the furnace and provide by ArcelorMittal. We have also included a cursory economic analysis based on fuel prices that you have given us during our meeting at your location on 4 April 2012. We provide this information so that a business case comparison can be made between each of the options being presented. At the conclusion of our analysis, we feel that the subject furnace can operate with a greatly reduced furnace pressure, exclude the use of Natural Gas and Oxygen, and reduce the amount of Blast Furnace Gas being consumed by the furnace. Implementation of any of these options will reduce furnace operating and maintenance costs. The next step of this project would be for ArcelorMittal to decide which option meets their future operating criteria best; taking into account financial hurdle rates, limitations to capital expenditures, future demand for products and the overall business objectives of the ArcelorMittal Corporation. Once this decision is made, Bloom Engineering will further refine our budgetary proposal taking into account your specific requirements and issue a more firm proposal with commercial guarantees. We are looking forward to working together with you to come up with the right solution to achieve the results that you are looking for

Very truly yours, Bloom Engineering Company, Inc. Dave Toocheck Associate Vice President – Business Development

Confidential Page - 2 - 11/30/2016



Executive Summary: Problem solving methodology: Using the observed production rate and temperature data that was collected while we observed the furnace we generate a base model for acceptable steel quality and observed fuel rates. We then use this information, to run several transient analyses to determine how the furnace would perform at different production rates, and with different types of burner arrangements. Our experience has shown that this method is valid for this application. The production rate of the furnace for the observed case was 96 mTPH. Our first challenge was to construct the heating curve of the steel for the observed case. We were asked to specifically analyze the following items, in the priority shown:

1. Reason for high furnace pressure and how to fix this. 2. Reduce gas consumption and operating costs 3. Improve yield 4. Remove bowing while maximizing the rate of production

To assist us in solving these problems we have ran six different scenarios, evaluating each of the scenarios for improved fuel rate and minimizing waste gas flow.

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5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The different cases are as described below:

• Case I - Evaluation of the furnace at the design throughput of 140 MTPH

SOAK ZONE

CASE 1

HEAT ZONEPREHEAT ZONE

• Case II - Conversion of the preheat

zone to regenerative firing at the observed throughput of 96 MTPH

SOAK ZONE


• Case III - Conversion of the preheat

zone to regenerative firing at the design throughput of 140 MTPH.

SOAK ZONE


• Case IV - Conversion of the preheat

and heat zones to regenerative firing at the observed throughput of 96 MTPH.

SOAK ZONE


• Case V - Conversion of the heat

zone to regenerative firing at the observed throughput of 96 MTPH.

•

SOAK ZONE


Case VI - Conversion of the bottom soak zone to regenerative firing at the observed throughput of 96 MTPH.

SOAK ZONE




5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The following tables are submitted to summarize options for each priority:

1. Recommendations to reduce furnace pressure, evaluated at 96 mTPH: a. The furnace as observed showed signs of elevated furnace pressure. b. Additional data provided by ArcelorMittal indicated that the measured oxygen concentration in the stack was between 8-10%. Where we would expect would be

an oxygen concentration of between 2 – 3% when a furnace is operating at an air to fuel ratio of 10% excess air. In the course of our analysis we found that there was agreement between the modeled fuel usage and the observed fuel usage, which implies that there must be infiltration of air somewhere between the furnace and the measured location. From our experience, we feel that the air recuperator is either leaking significantly or the oxygen concentrations downstream of the recuperators (at the measuring point) are being elevated due to other factors.

c. Using the ArcelorMittal supplied data for measured oxygen concentrations; we would also note that by calculation, each of the zones are running consistently without sufficient air for complete combustion. All of the data indicates that each of the zones are running rich, however, what is not known is the amount of Oxygen that is being used which can change the calculated air to fuel ratios. What can be determined from the data below is that the Oxygen concentrations being measured in the flue are too high. Operating the furnace at correct air to fuel ratios and identifying the location of air infiltration would reduce furnace pressure.

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d. One method to decrease furnace pressure, assuming there is no other outside air infiltration is to reduce the amount of gasses being supplied to heat the product. One way to do this would be the implementation of regenerative burners. In our analysis, we used a special regenerative burner with two media cases, one media case will heat the air, and the other will heat the fuel.

Zone 1 Zone 2 Zones 3 &4 Zone 5 Total TPH Fuel Rate Case Identifier Description GCal/h GCal/h GCal/h GCal/h GCal/h

(Kcal/Kg)

Observed 10.378 9.133 2.410 10.224 32.145 96 334.02 I Design 17.750 11.711 5.310 12.099 46.870 140 334.77 II Regenerative Preheat 5.004 9.206 2.292 10.115 26.616 96 277.35 III Regenerative Preheat @ 140 mTPH 8.721 12.443 4.970 11.711 37.845 140 270.02 IV Regenerative Preheat & Heat 6.926 4.101 2.292 10.117 23.436 96 244.55 V Regenerative Heat zone 11.334 4.046 2.292 10.115 27.787 96 289.29 VI Regenerative Bottom Soak zone 11.240 10.346 3.999 3.855 29.440 96 306.62 Regenerative inputs in red.

Summary of expected fuel rate, waste gas temperatures and waste gas flows. Evaluated at 96 mTPH only.

Conclusion: From the tables shown above, one can observe that the implementation of regenerative burners can reduce the quantity of waste gas being exhausted through the stack. By reducing the volume of waste gasses through the stack, the furnace pressure will decrease. The reduction in the flow of waste gasses varies between 17% – 29%. This reduction in waste gasses going out the stack will improve furnace pressure by 2 – 5 times from present conditions.

Production Rate

Fuel Rate Δ Fuel Rate from Case I

Waste Gas Temp.

Waste Gas Flow

Δ Waste gas flow from Case 0

Δ Stack Calc (infiltration w/o pressure control)

Improvement to furnace pressure from Case 0

Case Identifier

General Scope MTPH kCal/kg % °F SCFH % “w.c. %

Case 0 Observed 96 334.02 0.0% 850 2,148,975 0% 0.5625 0 Case II Regenerative Preheat Zone 96 277.35 17.0% 1,310 1,521,270 -29% -1.3811 346 Case IV Regenerative Preheat Zone +

Regenerative Heat Zone 96 244.55 26.8% 1,145 983,052 -54% -2.1523 483

Case V Regenerative Heat Zone 96 289.29 13.4% 1,373 1,661,684 -23% -0.7622 236 Case VI Regenerative Bottom Soak Zone 96 306.62 8.2% 1,423 1,773,002 -17% -0.3578 164




2. Reduce consumption of operating gasses with priority given to the most expensive gas (Natural Gas). a. Theoretical flame temperatures:

i. Flame temperature of natural gas and 10% excess air = 3460°F (basis of comparison)

ii. Flame temperature of Blast Furnace Gas only and 10% excess air = 2310°F (insufficient for heating steel)

iii. Flame temperature of Blast Furnace Gas, 10% excess air, 5% oxygen, air temperature: 421°C, and Blast Furnace Gas preheated to 234°C = 3397°F. This is the observed conditions. Shown graphically below.

iv. Flame temperature of condition iii without 5% oxygen = 3263°F (sufficient to heat steel)

b. Based on our analysis regarding theoretical flame temperature estimates, oxygen

enrichment and natural gas usage, which is currently being used on this furnace, can be eliminated as long as the air preheat and fuel preheat temperatures do not drop below 421°C and 234°C. This situation can only exist when the furnace is at operating temperatures.

c. Dual bed regenerative burners can preheat both the air and the gas to (process temperature – 150°C). Using the average zone setpoint for the Heat zone (1150°C), the theoretical flame temperature would be 3438°F, which is only 12°F of a natural gas flame, and very sustainable for a reheat furnace. Graphic below.

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5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] Basic Economic Analysis of the options: The table below summarizes production and fuel rates as well as a preliminary economic analysis of each of the studied cases:

Fuel & Oxidizer Costs

Production Days/year 200

Blast Furnace Gas (R$/Nm3)

R$ 0.02870

Furnace Utilization (%) 80%

Natural Gas (R$/Nm3)

R$ 0.7132 Oxygen (R$/Nm3)

R$ 0.2260

Heating Value of BFG (HHV) 900 Kcal/Nm3

Oxygen as a % of Blast Furnace Gas 5.0%

Production Rate

Fuel Rate

Δ Fuel Rate from

Case 0 Annual

Production

Cost Savings from Blast

Furnace Gas

Additional Cost Savings

from NO oxygen

Additional Cost

Savings from NO

Natural Gas

Potential Increase to Cash Flow

General Scope MTPH kCal/kg % (mTPY) ($R) ($R) ($R) ($R)

Observed 96 334.02 0.0% 368,640 - -

- Regenerative Preheat Zone 96 277.35 17.0% 368,640 666,185 1,546,005

2,212,190

Regenerative Preheat Zone + Regenerative Heat Zone 96 244.55 26.8% 368,640 1,051,766 1,546,005

2,597,771 Regenerative Heat Zone 96 289.29 13.4% 368,640 525,824 1,546,005

2,071,829

Regenerative Bottom Soak Zone 96 306.62 8.2% 368,640 322,101 1,546,005

1,868,106 Assumptions used in preparing the above table:

1. Natural Gas, Blast Furnace Gas and Oxygen Prices: As shown 2. Calorific content of Natural Gas: 8950 kCal/Nm3; Calorific content of BFG: 900 kCal/Nm3 3. Annual Production -= mTPH x Furnace Utilization x Production Days/year x 24 hrs/day 4. Potential Fuel Savings (BFG) = ∆Kcal/Kg x mTPY x 1000 kg/Ton x 1/900 kCal/Nm3 5. Potential Oxygen cost savings: = Potential Fuel Savings (BFG)*0.05*$R/Nm3 (Oxygen)

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5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The table below summarizes the estimated equipment and installation costs, and any potential increases to cash flow to determine a simple payback period.

Case Identifie

r General Name

Estimated Equipment

& Engineering

Costs

Estimated Installation

Cost

Estimated Total

Cost

Minimum Potential

Increase to Cash Flow

Simple Payback Period

($R MM) ($R MM) ($R MM) ($R MM) (years) Case II Regenerative Preheat Zone 1.948 1.948 3.896 2.21 1.76 Case IV Regenerative Preheat Zone

+ Regenerative Heat Zone 3.36 3.36 6.72 2.60 2.59

Case V Regenerative Heat Zone 1.948 1.948 3.896 2.07 1.88 Case VI Regenerative Bottom Soak

Zone 1.948 1.948 3.896 1.87 2.09

Assumptions used in preparing the above table: Ratio of equipment and Engineering costs to Installation costs: 1.0 General Scope of Supply: Case II (regenerative burners in the preheat zone only):

• 2 pair – (4) 1150-150/100/150 dual bed (air preheat and fuel preheat) regenerative burners rated at 3GCal/hr each for a total zone capacity of 6 GCal/hr. Burner price includes all necessary cycle valves, air and gas zone control valves, pilot equipment, new combustion air blower, new exhaust blower, new gas train for the regenerative zone, UV detectors on the main and pilot burners, self-standing control panel with factory mounted PLC and HMI screen, all necessary run-time software licensing.

• All necessary drawings for engineering of air, gas, and exhaust system piping • Excluded from scope of supply:

a) Any and all field installation b) All interconnecting piping between burners and blower (pressure or

exhaust) c) Any wiring from any electrical device to the main panel d) Motor starters e) Integration of new system into existing control system f) New gas train for conventionally fired system (if required) g) Field installation supervision, start-up, commissioning and training h) Periodic preventative maintenance contract for new system

Any changes that may be required to the furnace chimney

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Case IV (regenerative burners in the preheat AND heat zones): • Preheat zone: 2 pair – (4) 1150-150/100/150 dual bed (air preheat and fuel

preheat) regenerative burners rated at ≈3GCal/hr each for a total zone capacity of 6 GCal/hr Heat zone: 2 pair – (4) 1150-150/100/150 dual bed (air preheat and fuel preheat) regenerative burners rated at ≈4.2 GCal/hr each for a total zone capacity of 8.4 GCal/hr. Burner prices include all necessary cycle valves, air and gas zone control valves, pilot equipment, new combustion air blower, new exhaust blower, new gas train for the regenerative zone, self-checking UV detectors on the main and pilot burners, self-standing control panel with factory mounted PLC and HMI screen, all necessary run-time software licensing.



exhaust) c) Any wiring from any electrical device to the main panel d) Motor starters e) Integration of new system into existing control system f) New gas train for conventionally fired system g) Field installation supervision, start-up, commissioning and training h) Periodic preventative maintenance contract for new system i) Any changes that may be required to the furnace chimney

Case V (regenerative burners in the heat zone only):

• 2 pair – (4) 1150-150/100/150 dual bed (air preheat and fuel preheat) regenerative burners rated at 2.43 GCal/hr each for a total zone capacity of 4.86 GCal/hr. Burner price includes all necessary cycle valves, air and gas zone control valves, pilot equipment, new combustion air blower, new exhaust blower, new gas train for the regenerative zone, UV detectors on the main and pilot burners, self-standing control panel with factory mounted PLC and HMI screen, all necessary run-time software licensing.



exhaust) c) Any wiring from any electrical device to the main panel d) Motor starters e) Integration of new system into existing control system f) New gas train for conventionally fired system (if required) g) Field installation supervision, start-up, commissioning and training h) Periodic preventative maintenance contract for new system

Any changes that may be required to the furnace chimney




Case VI (regenerative burners in the heat zone only): • 2 pair – (4) 1150-150/100/150 dual bed (air preheat and fuel preheat)

regenerative burners rated at 2.43 GCal/hr each for a total zone capacity of 4.86 GCal/hr. Burner price includes all necessary cycle valves, air and gas zone control valves, pilot equipment, new combustion air blower, new exhaust blower, new gas train for the regenerative zone, UV detectors on the main and pilot burners, self-standing control panel with factory mounted PLC and HMI screen, all necessary run-time software licensing.



exhaust) c) Any wiring from any electrical device to the main panel d) Motor starters e) Integration of new system into existing control system f) New gas train for conventionally fired system (if required) g) Field installation supervision, start-up, commissioning and training h) Periodic preventative maintenance contract for new system i) Any changes that may be required to the furnace chimney

Interpretation of Results: Observed Case: The observed case is used as the basis for comparison to the other modified cases analyzed. Data from the observed case was collected in the field during the days mentioned in the technical report. This data was then used to construct a mathematical model of the actual furnace observed. During our days observing the furnace, neither natural gas nor oxygen was used in heating steel at the production rate observed. Dual Bed Regenerative Burners in the Preheat Zone (Case II): Based on our analysis conversion of the preheat zone to dual bed regenerative burners will reduce fuel rate from the observed conditions by 17%, reduce the amount of waste gasses by 29%, improve furnace pressure by 346% and shows the shortest economic payback for the cases analyzed (1.76 years). The only negative that we see in selecting this option is that if natural gas and oxygen were removed from the furnace initial heat up times can be extended. Fuel savings for this option can be increased by implementation of a cascade control system for these burners. A cascade control system will extend the unfired furnace length during periods of production that are less than the cases evaluated. We suggest further evaluation of this option. Dual Bed Regenerative burners in the Preheat zone & the Heat Zone (Case IV): Based on our analysis conversion of the preheat zone to dual bed regenerative burners will reduce fuel rate from the observed conditions by 26.8%, reduce the amount of waste gasses by 54%, improve furnace pressure by 483% and provides an economic payback of 2.59 years. The only negative associated with this option is that the calculated payback period exceeds the traditionally acceptable value of less than two years; however, further analysis of this option at lower production rates could provide much greater fuel savings and improve the payback period. This option also allows the operator to alleviate the use of natural gas and



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] oxygen throughout the operating range of the furnace. Cascade control can be extended so that both the preheat and heat zones can be cascaded off during slow production periods and delays, thus providing much better fuel rates. This option also allows the user to heat the furnace more quickly. Implementation of this option provides the greatest flexibility to furnace operations and we strongly suggest further evaluation. Dual Bed Regenerative burners in the Heat Zone only (Case V): Based on our analysis conversion of the heat zone to dual bed regenerative burners will reduce fuel rate from the observed conditions by 13.4%, reduce the amount of waste gasses by 23%, improve furnace pressure by 236% and shows a traditionally acceptable economic payback of 1.88 years. We see no negatives associated with implementation of this option. We suggest further evaluation of this option. Dual Bed Regenerative burners in the Bottom Soak Zone only (Case VI): Based on our analysis conversion of the heat zone to dual bed regenerative burners will reduce fuel rate from the observed conditions by 8.2%, reduce the amount of waste gasses by 17%, improve furnace pressure by 164% and shows a marginally acceptable economic payback of 2.09 years. This option does not offer as much to the operator as the options presented in Case II or Case V. Conclusions: We have been asked to evaluate this furnace for the following things:

1. Reduce the furnace pressure 2. Reduce operating costs 3. Improve yield 4. Remove bowing

1. Reduce the furnace pressure: After our evaluation, we have concluded that an

acceptable flame temperature can be provided at operating conditions to sustain furnace temperatures without the use of oxygen or natural gas. By reducing the volume of these gasses going into the furnace, furnace pressure will be reduced, however, during our observations, neither oxygen or natural gas were used at operating conditions, but, the furnace pressure was still high. A further reduction to furnace pressure will be to further remove the amount of gasses going into the furnace, and remove any infiltrated air in the stack (recuperator leakage). We can reduce the volume of gasses going into the furnace and improve fuel rate by implementing dual bed regenerative burners.

2. Reduce operating costs: Our analysis indicates that neither natural gas or oxygen need to be used during normal furnace operation, however, initial heat up time may be extended by removing these two gasses. Initial heat up time can be reduced, fuel rate will improve, and furnace pressure will improve greatly by installing dual bed regenerative burners as outlined in one of the cases above.

3. Improvements to yield: The scale losses for this furnace have been reported to be 0.7%, which in our experience is a little higher than the benchmark. Scale is a function of time at temperature. It has been reported that the mill associated with this furnace has extended delays. This is not helping improve yield. During delay periods, the furnace temperature must be turned down to reduce scale formation. A




properly implemented cascade control system will reduce the scale losses of this furnace. For a more detailed analysis of scale and scale loss as it relates to this furnace, see the technical report of this study.

4. Remove bowing: Our analysis shows that in all the cases evaluated the billets would be susceptible to bowing. The best way to minimize the bowing would be to shut off the preheat zone during conditions of limited production, or by implementing a cascade control system in the preheat zone. Bowing can further be reduced by the addition of cascade control in the heat zone.

We found this furnace to be in very good condition and it was operated in a very professional manner. We also found that the Engineering and Maintenance staff associated with the operation of this furnace to be very professional and accommodating to our requests. We thank them for their cooperation. Again, we thank you for the opportunity to allow us to showcase our analytical abilities and would welcome an opportunity to discuss our findings with you. The basis for our next discussion would be a review of this report, answering any questions, and hearing any feedback that you may have and then discussing the next step(s) in order to make this furnace the benchmark of the ArcelorMittal Corporation.




FOR:

Furnace Study Arcelor Mittal Monlevade, Combustol built Billet

Reheat Furnace

Bloom Project –BBO-2012-153 Steven O’Connor David Toocheck

May 16, 2012

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INTRODUCTION

The furnace is a walking hearth furnace used to reheat billets prior to rolling. It is top fired from three roof zones and bottom fired in the soak zone. The furnace was built by Combustol in 1986. It is fired with hot air and fuel from five separate zones of control with the last zone being a bottom soak zone. The furnace was originally designed for a production of 140 Metric Tons per Hour, however during our observations the production was 96 Metric Tons per Hour.

PURPOSE

The primary purpose of this study is to investigate the possibilities for upgrading the furnace for a production of 50 metric tons per hour with cold charging. To this end, various aspects of furnace operation will be addressed. These will include: • Heating Practice • Burners • Final Heating Quality

• Furnace Drafting

• Billet Bowing

• Fuel Quality

• Oxygen Enrichment Wherever practical, modified cases will be developed to illustrate the thermal advantages. Various fuel saving cases will also be presented as well.

CONCLUSIONS AND RECOMMENDATIONS

Regenerative burners will be required to improve furnace evacuation as well as to improve fuel usage and possibly to increase throughput while improving evacuation and fuel usage. Oxygen enrichment has little effect on fuel usage, efficiency, and flame temperature Recuperator maintenance has a profound effect on the operation of this furnace. The recuperators should be checked for leaks and corrosion. A Wobbe analyzer would be useful for minimizing excess air.

EXISTING PRACTICE The furnace is a top fired walking hearth furnace that heats 155mmX155mm billets 11300mm long. There are four zones of control along the length of the top of the furnace with the top soak zone subdivided into two sections across the width. There is also one zone beneath the top soak zone and part of the top heat zone.


The furnace is fired with blast furnace gas with an assist from oxygen. Natural gas is also introduced to assist combustion during high demand. Oxygen is never used when natural gas is in use. There are roof fired burners on the top zones and longitudinally fired burners from the discharge end on the bottom zone. Both fuel and air are preheated. From two separate recuperators in the flue.

OBSERVED CASE

GENERAL An observed case was developed based on field observation. On February 7 and 8, 2012, Bloom personnel were at the Mittal Joao Monlevade facility to make these observations. The following is a schematic diagram of the furnace as observed:

SOAK ZONE

32 METERS EFFECTIVE LENGTH

GIVEN PROFILE 96 MTPH



TRANSIENT ANALYSIS OBSERVED CASE A transient analysis was developed for the observed operation. The parameters were based on field observation. The following are the parameters used in developing this transient analysis: • 1020 °C Preheat Zone Setpoint • 1100 °C Heat Zone Setpoint

• 1155 °C Soak Zone Setpoint

• 1121 °C Bottom Zone Setpoint • 1134 °C Discharge Temperature • 96 Metric Tons per hour

• 20 °C Charge temperature • 160mmX160mmx11300mm long billets • Carbon Steel • 32000mm Effective Length • 13400mm Inside Width

The following is the resultant heating curve from this transient analysis:


HEAT BALANCE OBSERVED CASE

A heat balance was performed to establish thermal inputs and to verify the transient analysis. The following are the parameters used in developing this heat balance:

• Blast Furnace Gas Firing (900 Kcal/NM³)

• 10% Excess Air • 421 °C Air Preheat

• 234 °C Fuel Preheat • 830 °C Waste Gas Temperature

• 5% Oxygen Enrichment (5% of BFG Volume)

The following table shows the results of this heat balance:

FUEL RATE: 334.02 Kcal/Kg


DISCUSSION

HEATING PRACTICE AND HEATING QUALITY The furnace was designed to minimize bowing. The bottom firing in the soak zone encourages later heating. The heating practice chosen minimizes bowing with an artificially lower temperature setpoint in the preheat zone. The soak zone must compensate for the thermal deficiency in the heat zone by firing harder in order to make the heating quality. This is easily accomplished by the underfired burners in the bottom soak zone. FURNACE DRAFTING The furnace at its observed tonnage is drafting with the damper fully open. The damper is welded open and there is no control on the pressure in the furnace. The only way to improve this situation is to reduce the volume of gases in the furnace. This can be done with regenerative burners as described below. By replacing the preheat zone roof burners with two pair of dual regenerative burners the waste gases handled by the furnace could be considerably reduced thereby allowing the furnace to draft properly. The throughput may also be adjusted higher to optimize the drafting of the furnace with production. BURNERS Regenerative burners are typically installed in pairs. When one burner fires, the other burner pulls furnace gasses through the burner head, media and media case. The hot furnace gases transfer heat to the media where it is stored until the cycle reverses. After reversal, the burner that was firing becomes the flue, while the burner that was exhausting now begins to fire. The cold combustion air passes through the heated media where the stored energy is recovered. Air preheat levels within 100ºC-200ºC of the products of combustion in the furnace are typically achieved, while the waste gases are exhausted at a temperature of 200-250 ºC making the regenerative burners extremely efficient. By taking care of most of their waste gases, the regenerative burners reduce the overall gases going to the flue and stack. For blast furnace gas dual regenerative burners should be considered. These burners still use the regenerative concept as described above, but they have two separate media cases; one for heating air and one for heating fuel. This will allow the dual regenerative burner firing blast furnace gas to achieve the same performance as a standard regenerative burner firing natural gas.

MODIFIED CASES

GENERAL

In order to properly evaluate the furnace, the design throughput must be evaluated on the furnace as it presently exists. Once the parameters for this are established other cases can be developed. We understand that the furnace operates at 96 MTPH which is lower than the throughput that it is designed for, but in order to get a true feel for the capabilities of the furnace, we must consider certain cases at 140 MTPH. The major thrust will be to reduce the gas volume in the furnace, thus improving the furnace drafting. This is easiest accomplished by regenerative burners. Once a zone is converted to


regenerative firing, increased throughput can be evaluated to optimize the gas volume in the furnace with production. The following modified cases will be considered:

• Case I - Evaluation of the furnace at the design throughput of 140 MTPH • Case II - Conversion of the preheat zone to regenerative firing at the observed

throughput of 96 MTPH.

• Case III - Conversion of the preheat zone to regenerative firing at the design throughput of 140 MTPH.

• Case IV - Conversion of the preheat and heat zones to regenerative firing at the observed throughput of 96 MTPH.

• Case V - Conversion of the heat zone to regenerative firing at the observed throughput of 96 MTPH.

• Case VI - Conversion of the bottom soak zone to regenerative firing at the observed throughput of 96 MTPH.


The following are schematic diagrams of the modified cases:

SOAK ZONE


MODIFIED PROFILE 140 MTPHCASE 1


SOAK ZONE




SOAK ZONE



HEAT ZONEPREHEAT ZONE SOAK ZONE




SOAK ZONE



HEAT ZONEPREHEAT ZONE SOAK ZONE





5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] TRANSIENT ANALYSIS MODIFIED CASE 1 A transient analysis was developed for the first modified case. The parameters are consistent with field observation. The following are the parameters used in developing this transient analysis: • 1071 °C Preheat Zone Setpoint • 1127 °C Heat Zone Setpoint




The following is the resultant heating curve for this transient analysis

Page - 22 - of 46



HEAT BALANCE MODIFIED CASE 1



• 10% Excess Air • 421 °C Air Preheat where applicable

• 234 °C Fuel Preheat where applicable • 710 °C Flue Temperature



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5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] TRANSIENT ANALYSIS MODIFIED CASE 2 A transient analysis was developed for the second modified case. The parameters are consistent with field observation. The following are the parameters used in developing this transient analysis: • 1020 °C Preheat Zone Setpoint • 1100 °C Heat Zone Setpoint







5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] HEAT BALANCE MODIFIED CASE 2





• Regenerative Preheat Zone

• 90% Pullback on Regenerative Burners





5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] TRANSIENT ANALYSIS MODIFIED CASE 3 A transient analysis was developed for the third modified case. The parameters are consistent with field observation. The following are the parameters used in developing this transient analysis: • 1071 °C Preheat Zone Setpoint • 1127 °C Heat Zone Setpoint












• Regenerative Preheat Zone






5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] TRANSIENT ANALYSIS MODIFIED CASE 4 A transient analysis was developed for the fourth modified case. The parameters are consistent with field observation. The following are the parameters used in developing this transient analysis: • 1020 °C Preheat Zone Setpoint • 1100 °C Heat Zone Setpoint












• Regenerative Preheat and Heat Zones



FUEL RATE: 244.55 Kcal/K



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] TRANSIENT ANALYSIS MODIFIED CASE 5 A transient analysis was developed for the fifth modified case. The parameters are consistent with field observation. The following are the parameters used in developing this transient analysis: • 1020 °C Preheat Zone Setpoint • 1100 °C Heat Zone Setpoint












• Regenerative Heat Zone




Confidential Page - 31 -


5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] TRANSIENT ANALYSIS MODIFIED CASE 6 A transient analysis was developed for the fifth modified case. The parameters are consistent with field observation. The following are the parameters used in developing this transient analysis: • 1020 °C Preheat Zone Setpoint • 1100 °C Heat Zone Setpoint












• Regenerative Bottom Zone







DECARBURIZATION AND SCALING

Both decarburization and scaling are heavily dependent on time and temperature. Of these two, time is usually the more dominant factor so it stands to reason that the higher tonnage in the same furnace will lower decarburization and scaling. The following curve shoes decarburization in the furnace.



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The following curve shows scaling in the furnace:

BOWING

When heating from one side only, the product will experience a top to bottom temperature that is very large. The thermal expansion on the top surface will cause the billet to rise if this differential gets too high and the length of the billet could take the shape of an archers bow. Bowing is difficult to evaluate. The most pragmatic approach would be to establish the maximum temperature differential during the heating process on the observed case and make every effort not to exceed it on the modified cases. The critical situation for bowing is when the bottom temperature of the billet is between 400 and 800°C. Above 800°C, the billet is fully transformed into Austenite and bowing is not an issue.



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The following curve shows the overall susceptibility for bowing for the pieces in this furnace:

It can be seen from the above graph that all cases are susceptible to bowing. The only way to further alleviate the bowing problem, the preheat zone input must be minimized. The ultimate way to minimize bowing would be to shut off the preheat zone.



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The following is the heating curve to affect this minimized bowing.



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The following is the resulting heat balance for this heating curve:

FUEL RATE: 306.48 Kcal/Kg The following is the bowing susceptibility of the heating curve with particular attention paid to bowing. The same parameters apply to this curve as to the previous bowing susceptibility graph.

The bowing susceptibility is better here but bowing still could occur. The overall exposure to bowing, which is measured by time in the bowing range, is less.




EVALUATION

FUEL USAGE The following tables summarize the fuel usage of the furnace for each individual zone.

Zone 1 Zone 2 Zones 3 &4 Zone 5 Total TPH Fuel Rate

(Kcal/Kg)

Observed 10.378 9.133 2.410 10.224 32.145 96 334.02

Design 17.750 11.711 5.310 12.099 46.870 140 334.77

Regenerative 5.004 9.206 2.292 10.115 26.616 96 277.35 Preheat Regenerative Preheat 8.721 12.443 4.970 11.711 37.845 140 270.02 with Production Regenerative 6.926 4.101 2.292 10.117 23.436 96 244.55 Preheat and Heat Regenerative 11.334 4.046 2.292 10.115 27.787 96 289.29 Heat Regenerative 11.240 10.346 3.999 3.855 29.440 96 306.62 Bottom

Regenerative inputs in red. All values in Gcal/Hr unless otherwise noted.



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] FURNACE DRAFTING AND PRESSURE This is a complex issue. The theoretical calculations closely followed the observed fuel usage. The measured oxygen in the stack was between 8% and 10% which is extremely high. This value cannot come from excess air since the fuel values matched and were calculated with low excess air. The furnace was checked for obvious infiltration points and none were found. The only conclusion that can be reached is that the air recuperator on the furnace is leaking heavily. This leakage will account for 40% additional volume to the stack. The observed data shows about twice as much air flowing as should be there, which supports this premise. All of this extra volume affects the drafting of the furnace. The pressure will become artificially high and the furnace gases will not evacuate properly. Regenerative burners will alleviate the drafting of the furnace considerably. Regenerative burners take a considerable amount of gases out of the furnace thereby alleviating furnace pressure. Each case was evaluated with and without leakage. The following are tables summarizing the furnace drafting. Because the furnace has difficulty evacuating the waste gases, the damper is always wide open so there is no pressure control. The exhaust system was evaluated under the following conditions:

• Theoretical without pressure control

• Infiltration from air recuperator without pressure control

• Theoretical with pressure control

• Infiltration from air recuperator with pressure control

In order to maintain pressure control under the current conditions of recuperator infiltration regenerative burners will be required to afford a chance of evacuating the furnace. This drafting analysis shows the furnace as observed without infiltration as being able to evacuate but once infiltration is introduced, evacuation becomes impossible. It also shows that the introduction of regenerative burners will alleviate the drafting problems even with infiltration.



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The following is a table showing the furnaces ability to evacuate under theoretical conditions without pressure control:

Negative delta values indicate that the system is evacuating. The evacuation is weak (furnace pressure will increase) for delta values greater than -0.25; in other words, the more negative the DELTA value, the better the furnace is drafting, which in turn lowers the furnace pressure.

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5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The following is a table showing the furnaces ability to evacuate under infiltrated conditions without pressure control:



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The following is a table showing the furnaces ability to evacuate under theoretical conditions with pressure control:



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] The following is a table showing the furnaces ability to evacuate under infiltrated conditions with pressure control:



5460 Horning Road • Pittsburgh, PA 15236-2822 • Phone: 412-653-3500 • Fax: 412-653-2253 • Email: [email protected] FURNACE FUEL QUALITY The composition and calorific value of the fuel is inconsistent. This results in the combustion being off ratio at times. This problem can be solved by the installation of a Wobbe analyzer with a PLC type control system to control to the data of the Wobbe analyzer. A mixing station that includes a Wobbe analyzer to analyze the incoming Blast Furnace Gas and another Wobbe analyzer downstream of the mix that can be used for control, will be a more accurate and repeatable way to solve problems with fuel quality and air to fuel ratio. OXYGEN ENRICHMENT The furnace as it is presently operated, utilizes oxygen enrichment. Oxygen usage can be up to 5% of the total blast furnace gas volume. This will reduce the air ratio from 0.74 to 0.47. Although this reduction in air ratio will enhance the flame temperature slightly, it will do little to enhance fuel savings since the waste gas volume only reduces from 1.58 to 1.51 resulting in a 1.9% savings in fuel by using oxygen. Notwithstanding these heat balance results, separate calculations on efficiency yield only a 2% gain in efficiency which would confirm the above number. Unless otherwise noted, all conventionally fired combustion considers oxygen enrichment in this study.

RESULTS

The recuperators are the main reason that the furnace is not evacuating. Fuel Savings with regenerative burners will be 8.2 - 26.8% by depending on which zones are converted. Oxygen enrichment contributes to only 1.9% fuel savings. Fuel quality can be improved with the implementation of a mixing station that includes a Wobbe analyzer.

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EQUIPMENT REQUIRED

For Case 2 (regenerative preheat zone only), two pairs of 1150-150 burners with 100 and 150 cases will be required. For Case 4 (regenerative preheat and heat zones) the same burners stated directly above will be required plus two additional pairs of 1150-150 burners with 100 and 150 cases will be required for the heat zone. For Case 5 (regenerative heat zone only), two pairs of 1150-150 burners with 100 and 150 cases will be required. For Case 6 (regenerative heat zone only), two pairs of 1150-150 burners with 100 and 150 cases will be required.

CONCLUSIONS AND RECOMMENDATIONS

Regenerative burners will be required to improve furnace evacuation as well as to improve fuel usage and possibly to increase throughput while improving evacuation and fuel usage. Oxygen enrichment has little effect on fuel usage, efficiency, and flame temperature Recuperator maintenance has a profound effect on the operation of this furnace. The recuperators should be checked for leaks and corrosion. A mixing station with a Wobbe analyzer to sense the Wobbe index of the blast furnace gas and another to maintain a specified Wobbe would improve fuel quality, air to fuel ratio control and possibly marginally improve fuel rate.



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