Gas Burner Optimisation

Hmmm can you be a little more specific please? what are you Optimising? the burner/nozzle arrangement, the heat exchange section, both or the relationship between the two?

The maximum flow is for what? The fuel gas or the working gas (the hot, burn't gas heating the oil), I presume it isn't the oil as its not in liquid measurements.

where are you ? how long have you got to complete? I presume you have something already built which you are altering?

The optimisation is general, everything!

However i am looking at the utility consumption.

The max flow is the current amount of air that needs to be heated at max use. This flow is then split into 2 streams and feeds 2 process streams. However over the last year this max has reduced from a max of 180m3/hr to the current 140m3/hr.

The system is already operating.

I have 3 months to complete

Do you remember your Thermodynamics and Fluid Mechanics. A valve to split the oil to heat separate air flows or a ducting system to split the air after it is heated, I like the idea to split the air more. As for heating the oil I am sure that if you look through the text books for the above courses you would get some good ideas. Text books aren't just for school.

The air splitting is not the issue. Already done thanks. I'm optimising the process so reducing the gas input is the key i think.

And unfortunately textbooks in my first language aren't available to me at the moment.

To do the calculations we need a little more detail. Here is a list of the information that is required in order to properly and completely engineer a solution.

Temperature of air to be heated.

Moisture content or relative humidity of air to be heated.

Temperature the air is to be raised by.

Heat transfer characteristics of the radiator that will be used to heat the air.

Specific heat for the oil.

Flow rate for the oil within the system.

Heat transfer characteristics of the gas burner.

Combustion characteristics of gas being burnt.

Without all this information the answer will just be guesswork.. If you can get all this information I will work the problem through step by step. If you can't get all the information post what you have and I will see if some educated guesswork can be used for the missing data.

One final question is are you familiar with a thing called a psychrometric chart?

Thanks for your input. At the moment i don't have much information but am trying to collect. Here's what i have so far

The gas enters the burner with a pressure of 1.6 bar.

Gas burner setpoint is 230 deg C. However, normal operation is an ON/OFF system where the system heats oil to 232 deg C, then turns off. When the temp. of the oil drops to 214 deg C, the burner starts.

(Should I be looking at replacing with a modulating system)

This oil circulates through a system to heat air.

This system is made up of 2 parts (2 systems)

First system

Air enters with a flow of 60.0 Nm³/min and with a temp. of 41,3 deg C, leaves at 167 deg C (151-176 deg C)

Second system

Air enters with a flow of 80.0 Nm³/min and with a temp. of 45,9 deg C, leaves at 192 deg C (186-194 deg C)

Note: Both these systems may/may not be on simultaneously

Also, in the last 6 months The amount of air in each system has been reduced by 20 Nm³/min. Therefore, i know the system can be improved.

The air enters through a dehumidifier before entering the system

And yes i am aware of psychrometric charts

I havn't done this for a long time so I will put everything down in detail and do it in a number of steps so if I make a mistake somebody can correct it before we go too far.

Your original post stated that the total flow through the heating elements was 140 m³Hr^-1 but you later stated that the individual flow rates were 60 Nm³min^-1 and 80 Nm³min^-1. I am unsure where the N which in the SI system is the abbreviation of Newtons, the measure of force, comes into it. Its usually a good Idea to stick with the base SI units wherever possible and the usual unit for time is a second. Secondly its normal to use multiples of 1,000, for example K = Kilo = 1000 and mili = m = 0.001. So Before I go any further I would ask you to confirm the flow rates and whether they are per minute, hour or second?

The individual flow rates are 60 Nm³min^-1 and 80 Nm³min^-1. I was not correct the first site. Thanks for spotting that!

All the information in that email is correct. However, other information is proving difficult to find. so assumptions can be made.

Thanks

After some thought and reading the posts of others.

Perhaps you should start by looking at the output only, that is the reason the air is heated, then look at the available heat sources and determine most appropriate fuel. this can be left as Gas, particularly if its natural gas. Then look at historical systems. then related systems such as engine supercharger intercooling systems. after all this you will have developed some ideas as to what systems are most efficient and where the current system falls down. for example, is the oil process necessary? can you use a gas to air heat exchanger like domestic ducted gas heaters? what are the waste and end products - Exhaust gas and heated air post use. Can you recycle the air in a loop or feed exhaust air through a heat exchanger to preheat entry air? can you use the hot exhaust from the main HE to power other equipment either internal or external to the system? Can the burner exhaust be added to the heated gas, negating the heat exchangers?

On the fuel side have a close look at methods of 'burning' the fuel. The device is very low temperature. while traditional burners might be ok perhaps you could increase effeiciency by slowing the burn rate and burning at a lower temperature using a Catalyst. Automotive Catalytic converters Reach up to 1000 degrees when lots of NOx is in the exhaust. you could pass the fuelgas through a heat exhanger made out of catalyst. this would keep the temperature even right across the heat exchanger and allowing 100% heat transfer (temperature is the same on Both sides of HE) in a small space. Heat exchanges work best when the gases are moving slowly so you should consider gas velocities as well as transfer rates when determining size.

For an easy to read English reference, try Corky Bells' Book on 'Supercharger system design for cars'. their is a big section on both fuel combustion and heat exchanger design with lots of practical tips. I tcosts about $30 US or 30% less of Amazon.co.uk (plus postage)

Hope it works out well!

"Perhaps you should start by looking at the output only"

What I plan to do is work backwards from the output step by step and calculate the energy that is either being use or lost at each step then look at where the greatest losses are. Unless you have the whole process laid out in front of you anything is guesswork. However without confirmation of the flow rates I can't even start.

The individual flow rates are 60 Nm³min^-1 and 80 Nm³min^-1. I was not correct the first site. Thanks for spotting that!

All the information in that email is correct. However, other information is proving difficult to find. so assumptions can be made.

Thanks for the help

First up I thought we should work out how much energy it is going to take to heat the air and from that we will now the power we need to supply. I tried to find an extended metric psychrometric chart but couldn't so we are going to need to do this numerically rather than graphically.

Density of dry air at 1013.2 Hpa and 40ºC = c = 1.100 Kgm^-3

Specific heat dry at 1013.2 Hpa and over given range = τ = 1,010 jKg^-1

So looking at the first unit we get

Flow₁ = 60m³min^-1 = 1m³s^-1 = 1.100Kgs^-1

Power₁ = Energy1 / Time = Mass₁ x τ x Δt₁ / sec

Power₁ = 1.1Kg x 1010 x (167º - 41.3º) / 1sec = 139.652.7 js^-1 ≈ 140Kw

And doing the same for system 2

Flow2 = 80m³min^-1 = 1.33m³s^-1 = 1.467Kgs^-1

Power₂ = Energy₂ / Time = Mass₂ x τ x Δt₂ / 1sec

Power₂ = 1.467Kg x 1010 x (192º – 45.9º) / 1sec = 216,422.8 js^-1 ≈ 220Kw

So that means we need to radiate 140Kw into system 1 and 220Kw into system 2 to get the temperature rise you are talking about.

Before we go any further dose this sound about right to you?

By the way you keep stating that the flow rate is 60 Nm³s^-1. What do you mean by the N? In SI units N is the abbreviation for Newtons and is the unit for force so you are saying is that the flow rate is 60 Newton cubic meters per second which doesn't make sense to me.

Optimization of a Gas Burner is a very big subject and gets expensive as you go along. Let me advice you on the cheapest methods first before I lead you to complex modes & expense.

1. First you must have a Gas Flow Meter & Electrical Meter for the Circulating Pump for, what you cannot measure you cannot monitor.

2. Ensure that all heat losing surfaces of the Oil Boiler, all pipes & flanges, valves are very very efficiently insulated.

3 . Insulate the Exhaust of the Machine minimum 4ft. and check if you can shut off the exhaust motor and fully open the damper.

4 . Ensure that there is no leakage from the side walls of the machine.

5 . Do you have the 3-way Temperature Control Valve Chamber-wise, else install.

6 . Buy a portable fuel efficiency analyzer to adjust air/gas ration - this saves 4% fuel.

Now the expensive part:

7 . Install a moisture meter and synchronize with Inverters to optimize the circulating blowers and simultaneously synchronize your circulating pump.

Further optimization & further expensive part:

8 . Pre-heat combustion air.

9 . Replace on/off burner with modulating burner with Oxygen Trim.

Thanks for all information so far!!!

To answer an earlier question the N in Nm3/min stands for 'normal conditions'.

A query... Because the airflow requiring heating has been reduced over the last year.

Does this mean that the oil doesn't need to be heated up to the same temp. as before - 232 C. While still maintaining rate of transfer and achieving the same temperatures!

No. Also to save on fuel try utilizing low pressure burners.

G'day Craig,

• "cut C O emissions 300 to 600%"

How can you cut or reduce something by 600%?

The way I was taught is that if you reduce something by 100% then there's nothing left so how do you reduce something by 300 to 600% ?

Do you mean that it was reduced to ¹/₃ (≈33% of the original level and a 67% reduction) or ¹/₆ (≈17% of the original level and an 83% reduction).

Also the CR-4 editor isn't too good at displaying chemical formulae so are you talking of CO (carbon monoxide) or CO₂ (carbon dioxide). As you undoubtedly know carbon monoxide is a by-product of incomplete and therefore inefficient combustion but decomposes into carbon dioxide rapidly when vented into the atmosphere. Carbon dioxide on the other hand is a green house gas and responsible for global warming.

Either way, you want to get every last Joule out of your gas so zero carbon monoxide is the goal wile minimal carbon dioxide is what we need to reduce the effect we are having on the earth's climates.

If you are managing to reduce CO₂ levels to a third or sixth of the norm then its an impressive reductions and a great achievement.

Regards, masu