Application: Arcelor Mittal Harriman Steel, Pusher Reheat Furnace

 

The amazing benefits of ITC Coatings are seen perhaps nowhere greater than when they are used in the relining of an industrial furnace or kiln. This case study includes the issues, methods and results of a very successful reheat furnace reline we performed for a major steel producer, helping them to reach their full production potential.

 

furnace reline crew

 

 

 

FURNACE DETAILS
• Furnace: The furnace is rated at 75 tons/hr. and utilizes Bloom high temperature burners
designed for 7500F combustion air with and utilizing a recuperator. The maximum Btu input is
89.9 MM Btu or 1.2 MM Btu/ton. The furnace controls are minimal with the system utilizing an
air lead only instead of a more precise lead lag system, and the exhaust utilizes a forced
evacuation fan with manually adjustable damper blades.

• Lining Configuration: Most of the existing refractory was in reasonably good shape except for
the billet charge, discharge peel bar and billet discharge openings, which were badly damaged.
The soak zone burner wall was also badly damaged.

• Customer Need: ITC recommended a solution to address several major challenges:

- Excessive heat loss and shell temperatures on the roof and sidewalls.
- High fuel consumption
- Continual refractory maintenance with charge and discharge openings

 

ITC RECOMMENDATION
• Engineered Approach: ITC recommended a hot face veneer to address the customers’
requirements. The veneer design included:

- 1” thick 12”x12” ceramic fiber squares (2300 F temperature use limit)
- A proprietary, high-reflectivity hot face coating

• High Reflectivity Coatings: ITC manufactures a proprietary, high reflectivity coating (ITC 100HT) to work in concert with the furnace conditions and veneer design. Under ideal conditions, high reflectivity coatings absorb energy from the process and re-radiate it to the furnace load, imparting the following benefits:

- Lower heat loss – Minimizes heat transfer through the furnace refractory walls
- Lower Maintenance costs – Protects the substrate refractory
- Improved furnace operation – Improves the thermal efficiency of the process
- Reduction in scale generation – Less Fe2O3 available due to more efficient burning
- Increased throughput – Additional energy (Btu’s) available to heat product at an increased rate
 

IMPACT ON THE PROCESS
• LOWER SHELL TEMPERATURES
The combination of veneer and the coating significantly lowered shell temperatures

• IMPROVED BTU SAVINGS
Due to the thermal efficiencies, Btu/gas savings was reduced by 20%

• LOWER OPERATING TEMERATURES
The thermal efficiencies of the new design enabled the operators to drop normal furnace
operating temperatures (as indicated by thermocouples) from 2150 F to 1840 F.

• INCREASED THROUGHPUT
By reflecting the energy back to the colder steel load in the furnace, the furnace throughput
increased from 65 tons to the rated 75 tons per hour.

• REDUCED SCALE/MORE PRODUCT
Decreased operating temperatures and increased throughput have allowed an increase in yield
of approximately 2 ½ % due to a significant decrease in scale generation. At full production this
amounts to 6,150 additional tons of saleable product per year.

• REDUCED AMOUNT OF ENERGY REQUIRED
Combining all efficiencies, the amount of energy required dropped from 1.2 MM Btu/ton to 0.96 MM Btu/ton. If the flue exhaust is restricted as is recommended and the burner control system updated, this furnace could attain 0.88 MM Btu/ton or a reduction in fuel usage of 33%
 

 

IMPACT ON BOTTOM LINE COSTS

• FUEL SAVINGS = $833,000 per year (at $8.00 per MM Btu)
Previous: (65 tons/hr.)(1.2 MM Btu/ton) = 1,872 MM Btu/day
New: (75 tons)(.8 MM Btu/ton) = 1,440 MM Btu/day

• INCREASED PRODUCTION = $2,929,500 per year
= (6,510 additional tons/year)($450 ton)

• ROI = 1.33 weeks (at full production of 6,000 hours/yr. or 15 turns/wk.)

TOTAL IMPACT/YEAR = $3,762,500
 

Corrosion & Prevention In Cement Plant Baghouses

A SUMMARY OF THE CAUSES OF CORROSION AND A PATH TO ITS ELIMINATION

Greg Odenthal, Director of Engineering & Technical Operations, ITC - International Technical Ceramics, LLC and Steve Williams, COO of JC Industrial Services, summarize baghouse corrosion and provide a solution for its elimination.

INTRODUCTION

Corrosion causes plant shutdowns, waste of valuable resources, loss or contamination of product, reduction In efficiency, costly maintenance, expensive over design and also can jeopardize safety. In general, corrosion In cement plants occurs when process gases containing moisture, SOx, HOI, and NOx, operate at dew point temperatures. The economic Impact of corrosion damage has become a significant problem In cement plants worldwide. The best time to stop corrosion Is before It begins and ITC - International Technical Ceramics, LLC has developed several ceramic thermal barrier coatings that have all but eliminated baghouse corrosion due to condensing flue gases.

CORROSSION PROCESS

Carbon steel and even stainless steel corrodes In flue gas service. Equipment like electrostatic preclpltators, baghouses,
cooling ducts, conditioning towers and stacks frequently fall due to corrosion. Corrosion Is worse when there is presence
of acidic compounds In the flue gas. Figure 1 shows severe corrosion on the Inside of a baghouse lined with conventional epoxy based coatings.

The source can be from sulfur content In the feed or fuel, chloride content In the feed or air and C02 and NOx from combustion. The moisture content in the gas stream produces hot acid condensation on the steel shell walls, and in most cases, intermittent for short periods of time however the cumulative impact can be up to 1.0 mm/yr. of metal loss equating to less than five (5) years life. This loss of metal thickness can be seen as thick rust flakes and also pinholes caused by localized attack.Atmospheric air entering the system through these pinholes gives rise to an increase in energy consumption during operation of the baghouse. Air pollution control devices, the fans and stack are also candidates for corrosion. Water spray towers used to control temperatures, amplify the problem. Some processes have acid gas scrubbers, which are also problematic if they are not protected. In these systems, the stack Is also a problem area. In general, equipment operating In the cooler end of the process is where most of the corrosion develops. These areas are sensitive to cold air in leakage, low external temperatures and startups and shutdowns.

The corrosion of pollution control devices in cement plants Is most severe during the acidic condensation of the process gases containing moisture, S03, S02, C02, HCI and NOx. The condensation can be more frequent and more aggressive depending on several variables such as moisture concentration, inlet gas temperature, defects in the thermal Insulation, leaks of cold air into the baghouse and low ambient temperature. When there Is a large fluctuation In the gas temperature entering the baghouse, an additional complication occurs; at lower temperatures there Is severe corrosion due to condensing flue gases, at higher temperatures there can be thermal degradation of the corrosion protection (conventional) coating.

CONVENTIONAL COATINGS

Many coatings have been developed in the past. Epoxy and sillcone coating materials can resist the effects of acid condensation to some degree. Acrylics, alkyds, or polyesters will not withstand high operating temperatures. The failure mode for these types of coatings are oxidative degradation and delamination, see figure 2. Oxidation damage occurs when the process equipment operates above 150° C (302° F). Undercut corrosion, dis-bonding and delamination occur when there is any surface damage or imperfection in the surface preparation. There are high temperature silicone coatings that can operate up to 500° C (932° F) in dry environments, but in hot combustion gas systems with even a small percentage of moisture content, they tend to fail in a few months.

CERAMIC COATING TECHNOLOGY

Today high temperature, energy efficient ceramic coatings are being used to eliminate baghouse corrosion along with the high cost of maintenance associated with this problem. ITC - International Technical Ceramics, LLC has engineered and developed several different ceramic coatings that are successfully being used to prevent baghouse corrosion. These coatings have no VOC's and are water based, spray applied products with excellent adhesion and the ability to handle high temperature, moist and acidic environments without de-bonding see figure 3.

Instead of applying a barrier that slows the heat conduction through insulation and substrate, ITC coatings use reflective, low transmittance technology to improve insulating values and prevent the formation of a dew point thus eliminating condensing flue gases and acid attack. Substrate surface preparation is critical to the success of ITC coatings and must be abrasively blasted to remove chemical debris and contaminants from the shell, which are the catalysts for the onset of corrosion. Application thicknesses for ITC coatings are only mills thick compared to 100+ mills of conventional epoxy-based coatings. ITC and its alliance partner JC Industrial Services to date, have several successful installations, each with two (2) to three (3) years service life without any metal loss or coating maintenance required. The major benefits attained through the use of ITC protective coatings are:

  • Baghouse longevity due to the elimination of metal loss
  • Reduction in downtime
  • Increase in efficiency due to elimination of condensing flue gases leads to reductions in bag and cartridge corrosion allowing for longer campaigns.

CONCLUSION

Despite the developments in corrosion resistant alloys over the past few decades, carbon and stainless steels continue to rust and corrode in harsh acidic environments. The need for corrosion prevention is greater today then ever before due to the new more stringent pollution and emission regulations imposed by the EPA. Without the use of coatings, surface substrates will continue to corrode leading to premature equipment failure costing hundreds of thousands of dollars per year in steel replacement, maintenance, unscheduled downtime and possible fines. lie provides a cost effective path toward corrosion elimination through the use of thermal barrier coatings that extend the service life of cement plant equipment.

 

 

REFERENCES:

1. "The Benefits of Internal Coatings" Debra Ashley - Specialized Coating Technology, LLC

2. "Solutions For Severe Corrosion" Linas Mazelka - 3L&T Inc. USA

Anchor Corrosion Testing Using ITC Coatings

A couple of years ago a lot of work was done on anchor corrosion from experiences in the cement industry where increased use of waste-derived alternative fuels leads to high levels of alkali chlorides and sulphates. The problem in the field still exists today. One issue is that the steel grades that apparently exhibit the greater resistance are those with the lower service limits i.e. generally too low for the environment in which we want to use them. Our current strategy is to modify the lining construction, limiting the possibility of gas tracking and minimize insulation to avoid dew point conditions and problems at the interface with the working lining. As a result of this ongoing problem, there is an increasing movement back to brick, contrary to the high tech monolithics available today.

There is strong momentum however behind the idea of ceramic coatings on anchors. We have been promoting our high temperature ceramic coating, ITC 213, which is specifically designed as a ceramic coating for metals. Aside from cement we are also getting involved in waste to energy and power applications, where there are similar issues.

ITC COATED ANCHOR CORROSION SAMPLES

METHOD

Castable pots made of silicon carbide (SiC) were core drilled and filled with 40g of a 60:40 molar mix of NaSO4 and NaCl respectively. Fourteen anchor samples were cut (two of each grade), half were coated in the ITC 213 alkali resistance coating, and all of the samples were placed into an individual pot covered with a SiC incineration tile lid. The ITC coating was easily applied; the anchors were rubbed with emery paper then rinsed in bleach. A sponge was used to lightly coat the anchor with the ITC 213 coating and the samples were left for 24 hours to dry. The pots were transferred to a furnace set to 900o C for 5 hours, the pots were removed once they had cooled and were visually inspected.

FINDINGS

As expected the samples with the higher content of nickel have corroded the greatest. The ITC 213 coating appears to have offered alkali corrosion protection to all the grades. For example theuncoated Inconel 601 has completely corroded however the ITC coated Inconel 601 still posses some of its original structure. From outward appearances it would appear that the ITC coating has been highly beneficial. A more detailed evaluation of the test pieces should reveal the full extent of the alkali resistance that the coating imparts to the stainless steel.

RESULTS

IMAGES

The images below show the outward appearance of the test samples.