Hot Flue Gas Cooling

I'd walk a mile for a Camel^®. And it might need to be even farther.

800º C?

With that kind of waste heat, you should be making it into electricity...removing heat in the process.

you need to rephrase your question or you'll continue to get answers on co-generation. are you asking about filtering?

Dear sir,

Thanks for your reply. this is lead smelter plant. In rotary furnace lead impure heated to particular temperature and melted and produce pure lead ingots. During this process flue gas ( with dust ) with 800 deg temp will come out. we have to filter this dust, lead fumes before leaving it to atmosphere. So hot fumes allowed to settling chamber and here due to low velocity lot of heavy particles will settle down. then this flue gas with dust passed to cyclone , here heavy particles will settle down. before passing this fume with fine dust particles to filter bag filter we have to reduce the temperature below 80 degree to protect the filter bags. for that only we are increasing the flue gas travelling distance by increasing the duct length. pls help me to find out any calculation for this heat transfer to atmosphere.

Dear sir,

Thanks a lot for your valuable reply. shall i have your mail is to discuss further.please.

The only methods to cool anything is to put a heat exchanger and have the product pass through it.

Having said that the exchanger needs to be sized in your case for flue gas solids deposits and for the thermal dissipation as well as for the low pressure of the flue gases.

Now then to perform this you can use a co generation system which will reuse the heat and turn it into electricity or you can use a set of cooling towers and / or cooling exchangers.

To develop this system you need to do the following:

1.- HIRE a professional who can analyze the best options and design the system.

2.- USE a professional contractor to install it.

3.- Since you have given us no real process data to review the best answers are guesses, which make us think you are either doing homework or have no technical knowledge to even asses issues like this.

Furthermore, there are filtering system for quite high temperatures.

Your post raises several questions that you would need to provide answers for. First, why is your furnace exhaust temperature so high? Are you sintering metal or calcining? This is much to high for drying. Second, why is your baghouse limited to 80 degrees (assuming Centigrade)? As noted by vargaalex there are filtering media that can operate up to 260 deg C (800 C for ceramic filters of special design), which would reduce your ducting requirements. As noted in several of the other posts, recovery of this heat would help minimize the costs, however, if this is not feasible, then to go to the heart of your question, for conductive/radiant cooling of this flue gas you need to know your temperatures, inside the ducting and outside. Calculate your heat loss across the duct metal using table heat transfer coefficients. Determine calorie/BTU heat loss required and divide by heat loss through duct wall (assuming no insulation) per square foot (sq. m). This will give you total duct wall area required and this can be converted to duct length. Issues to consider include protection since duct temperature will be extremely high, condensation issues based on moisture content in flue gas, and static loss of ducting system and its effect on conveying fan at the baghouse. Keep in mind gas viscosity is constantly changing which will affect frictional wall loss.

Senthill,

Are you going to join in the conversation of your own creation?

If not, then just take filter bags off and be done with it.

Dear Senthil,

If this only consult regarding reducing temperature of flue gas,

i would suggest to pass those flue gases through recupreator of the f/c if available or install new one. which can absorb heat of those gases and provide preheated air to the f/c burner. which can increase combustion efficiency and reduce fuel consumption.

here i assume burners are designed for hot air combustion.

as per i think you can reduce temperature of flue gases by 50-60% in this stage.

further to reduce temperature to 80deg. you have 2 options,

1. you better lengthen duct length up to bag filter.

2. Add an additional dialution damper in that duct.

dialution damper is just a round piece of duct. approx. double the OD of flue gas duct.

which is open from one side and other side is connected to bag filter duct.

here bag house sucks fresh air from atmosphere along with flue gases.

i hope it can work. i have already installed such systems.