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How do we improve the efficiency of a fired heater running on fuel gas and an fd fan?
 
Answers
23/07/2018 A: Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
In addition to the above, linking the FD Fan suction vane with the Flue Gas oxygen analyser will help in optimising the excess Oxygen that tend to lower the heat duty of the flames. Target of excess Oxygen can be derived to suit the stack emission targets. Ensuring that the gas burn in the radiation zone (prevent after burn in the convection zone) by ensuring the burner fitness will help. Blown off gas riser tips due to partial coking of Olefinic compounds in the Fuel Gas will push the burning to convection section. We have experienced complete coking and rupture of of gas riser tubes resulting in extremely bad flames. Healthy gas flames can be achieved by preventing fugitive air ingress from other than air registers, regular burner maintenance, ensuring Fuel Gas quality (optimise the C3 levels in Fuel Gas) etc.
18/07/2018 A: sagar dandekar, Bharat petroleum, sagar.girgaon@gmail.com
1. adjust fuel air ratio to optimum
2. check for air leakages in furnace box
3. do not keep main burner off (as it will change shape of burner holes if kept closed, these holes are specially designed for particular operating conditions)
4. calculate thermal losses through walls and flue gases ( try to recover energy through it )
5. preheat the combustion air.
18/07/2018 A: Mike Watson, Tube Tech International Ltd, mike.watson@tubetech.com
Robotically clean the external finned tube surface of the convection bank which guarantees all fouling removal from every row to reduce stack temperature, save energy and refractory / tube damage.
Internal de-coking is also vital to enhance heat transfer and production.
17/07/2018 A: Bruce Carr, Suncor Inc, bcarr@suncor.com
Despite what anyone tells you trying to run higher efficiency on any heater can be dangerous and harmful to the heater... A good flame pattern is the most important element in both safety and efficiency... Training the operators, as in actually going in the field and showing them, will be the most effective way to improve efficiency... It doesn't matter what your O2 analyzers tell you.... Training operators to run a heater on analyzers and draft gauges without a good knowledge of flame patterns and all the adjustment options available is a recipe for disaster. Good training will result in the best efficiency....
17/07/2018 A: keith bowers, B and B Consulting, kebowers47@gmail.com
First step is to measure 'excess air' and temperature of flue gas coming out the stack. Then measure for any unburned hydrocarbons or CO, which would indicate incomplete combustion due to poor mixing at burners, insufficient fuel atomization (liquid fuel),or plugged burner tips.
Presuming no unburned hydrocarbons and low/no CO, but high excess air, reduce the air into the furnace (heating extra nitrogen wastes fuel energy.)
Of course the external tube surfaces must be clean. If they are fouled with soot or scale deposits they will not conduct heat well.
The most common adjustment needed is to reduce the 'excess air' to the minimum needed for complete combustion. Research on-line for furnace management and excess air levels desirable.
Note the firebox of the furnace must be airtight--no air leakage into the firebox. ALL air must enter through and around the burners. The burners must be properly adjusted (both fuel pressure and air addition through and around the burners. Contact the burner manufacture for their recommendations for those
particular burners.
Be sure the flames do not impinge on the tube surfaces as damaging spot overheating will happen. Adjust the local burner(s) as necessary to prevent flame impingement.

The essence of efficiency improvement is reducing 'excess air' to minimum necessary, ensuring the tube external surfaces are free of any deposits (soot and or scale) and clean as required.

Internal tube surfaces also must be clean since fouling will reduce heat transfer to the process fluid. Sometimes steam addition to the /furnace tubes will improve the efficiency, but consult with the furnace manufacturer and burner manufacturer for their specific advice.

All of these suggestions do not involve adding convection section surface area of other capital costs. Often just cleaning the furnace tubes inside and out and adjusting the burners properly will result in design or better efficiency.
17/07/2018 A: Muhammad Akhtar, Orpic, mbadgk@gmail.com
If there is really issue with furnace efficiency than following things can be done
1) check for air leaks into the heater. If you sometimes air leaks in the convection zone and firebox lead to incomplete combustion of fuel while online analyzer showing excess oxygen as normal but actually it is not contributing towards combustion.
2) ceramic coating can be carried out on heater tubes and refractory to improve heat transfer rate. This improves the efficiency by 5 to 10% but requires capital investment.
3) installing a air pre-heater will help in improving the efficiency.
17/07/2018 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Keep the analyzers calibrated and minimize excess air.
17/07/2018 A: Ashutosh Garg, Furnace Improvements Inc, agarg@heatflux.com
A heater running on forced draft and fuel gas can operate on very low excess oxygen say 1-2% and that will improve the heater efficiency.
Flue gas temperature needs to be reduced leaving convection section to improve the heater efficiency and that means cleaning convection section or upgrading convection section.
Please visit our website www.heatflux.com and you will find several papers on improving heater efficiency.