5 replies to this topic

[6chemprocess]

Dear Experts

I am new to this process engineers forum. 

 

I am currently working on a mass and energy balance for a calcite type limestone rotary kiln with preheating tower. In the past, I did material-heat balances to calculate heat loss, unknown quantities. But  I  never done a M&E to calculate the unknown temperature. I am looking forward to seek some help to determine the methodology to calculate temperature of solid material from heat balance calculations.

 

I have attached a simple block diagram with parameters for your reference.

 

My main objective is to estimate the temperature of lime stone entering into the kiln from pre-heater & temperature of air entering the kiln.

 

In our plant, we don't have facility to take sample out of tower or no sample point between kiln and pre-heater.

So rate of conversion inside pre-heater is unknown and also the temperature of solid material,composition is unknown.

 

Please let me know if I can really find out of temperature of solid materials from heat balance. It looks like there are more unknowns than equations. 

 

It would be great if an expert can give me the methodology to solve the unknowns.

 

Unknowns:

1. Temperature of material coming out of kiln to cooler (solid material not gas) ?

2. Secondary air temperature above cooler and below burner is unknown? 

3. Stone feed temperature from pre-heater to kiln is unknown? I have to calculate by assuming some conversion and I don't know how much to assume (should i assume 0% or 10% or 20% conversion inside pre-heater)

4. Heat losses around pre-heater is unknown , heat loss around cooler unknown(may be I can assume no heat loss in cooler), kiln shell loss was measured using shell scan temperature measurement.

 

knowns:

1. Production data is known based on tonnes- I calculated the feed rate

2. Fuel flow rates (coal,gas)are known- I can work out stoichiometric air requirements and flue gas emissions.

3.Temperature of  raw materials, fuel from the plant such as stone feed at ambient conditions, fuels at standard condition for gas , for coal- temperature is known.

4. Primary air supplied by fan, cooler air supplied by fan is known.

5. Oxygen , CO at Kiln inlet and pre-heater exit is known.

6.Dust loss is assumed 

7. Feed end temperature (dust, flue gas from kiln outlet to pre-heater in)  is known 

8. From material balance - I can calculate false air leakage quantity.

9.composition of raw materials, products ,fuels are known.

 

 

Kind regards

sen

 

 

Attached Files

•  block_diagram1.pdf   202.39KB   48 downloads

[PingPong]

This is a lot for outsiders, so let's do this step by step.

 

First make a block flow diagram on which you only indicate the known parameters that were actually measured, and in the units that they were measured. Do not show what you estimated, (re)calculated, assumed.

 

You will also need the composition of the natural gas and the ambient air conditions.

 

You mention coal but I don't see that in the diagram, or do I overlook it?

If coal is added you need to know the actual composition of it, including ash and moisture content.

 

Obviously you need the specific heats of all compounds.

And you need the heat of reaction for all reactions taking place, or you need the standard heat of formation for all the reacting compounds (CaCO₃ et cetera).

 

If you want to estimate heat losses you need to know what the outside area of the equipments are and what kind of, and thickness of insulation and brick lining is used.

[breizh]

Hi ,

To me the best way is to use excel and issue a table with the mass balance and heat balance . As stipulated by Ping Pong a lot of data are missing to establish the heat balance .

In case of data missing , you may use an external equipment like Pyrometer to get access to the temperature, for example shell of the kiln , gas even products  .

 

The MS solver should help you to consolidate all your balances .

 

Good luck.

 

Breizh

[6chemprocess]

Hello Breizh

Many thanks for your reply. I will sketch them again.

Yes! I am doing it in excel using goal seek. I took all the CP, heat of combustion, heat of calcination from handbooks for heat balance. 

 

I am assuming conversion inside preheater(composition , exact flow rate is unknown)

 

Heat input+Heat of combustion=Heat output+Heat of vaporization+Heat of calcination(based on % of assumed conversion)+ heat loss

 

for preheater balance:

I don't know heat loss.

I am getting.

for example  an equation with unknown temperature and heat loss.

12kg/s*CP*(X-298)+40000 kW=300kW+heat loss(don’t have it- can I assume 5% of input)

Finally need temperature  X from preheater balance. X- solid temperature from lime stone(no facility to measure)

 

This X will be input for kiln heat balance to get the following equation.

 

12kg/s*CP*(Y-298)+40000 kW=300kW+5kg/s*CP*(Z-298)*heat loss(measured for kiln from shell scans)

 

On kiln heat balance

2 unknowns Y&Z. Y- solid temperature coming out of kiln and Z- air temperature –Access is a problem to measure temperature in correct location for secondary air.

[breizh]

Hi ,

Probably using the solver , specifying the constrains , you should get more realistic result . Let you try Pyrometer or Infrared Camera to get access to unknown temperatures , this should be a good initialization step for your Heat and Mass balances.

 

Note : Pyrometer or IR camera may be available in your Maintenance department  or can be rent .

 

Good luck.

Breizh

[PingPong]

 

for preheater balance:

I don't know heat loss.

I am getting.

for example  an equation with unknown temperature and heat loss.

12kg/s*CP*(X-298)+40000 kW=300kW+heat loss

Is that supposed to be the heat balance of the preheater? Surely you are joking.

 

 

 

This X will be input for kiln heat balance to get the following equation.

 

12kg/s*CP*(Y-298)+40000 kW=300kW+5kg/s*CP*(Z-298)*heat loss

Is that supposed to be the heat balance of the kiln? Surely you are again joking.

 

 

Fist step is to get the overall heat balane and the overall mass balance correct, including the overall mass balance of all the elements (H, C, O, N, Ca, et cetera).

 

First make a block flow diagram on which you only indicate the known parameters that were actually measured, and in the units that they were measured. Do not show what you estimated, (re)calculated, assumed.