Incinerator

[Bug6]

I am trying to simulate an incinerator for sludge on a ship. Basically, the incinerator is started by using a small amount of diesel. When that is up to a given temperature, the diesel is shut off and the sludge is allowed to flow through. There is a primary air fan which adds air to the mixture in order to increase the temperature and the burn efficiency.
I am not sure of the exact chemical reaction equation for the sludge, so I am using the calorific values of heavy fuel (which is mostly what the sludge is) and diesel in order to calculate the energy.
My equation for the energy inputs is:
mdot(sludge)*cv(sludge)+mdot(diesel)*cv(diesel)+mdot(air)*cp(air)*(Temp(air_final)-Temp(air_in))
My equation for the energy outputs is:
mdot(exhaust)*cp(exhaust)*(Temp(exhaust_out)-Temp(air_final))+k*A/L*(Temp(chamber_final)-Temp(chamber_begin))
I hope this makes sense. So, I know the values for everything but the Temp of the exhaust, the final Temp of the air, and the final Temp of the chamber.
Any ideas if I am following the correct train of thought? I am unsure what a second equation would be in order to solve for all the unknowns. Thanks in advance for the help.

 

[athomas236]

Heat in = Heat out + heat transfered to incinerator by radiation and convection.

Regards,

athomas236

 

[Bug6]

Which is exactly what I have, except I neglect radiation. I just have three unknown temperatures and one equation. Any other equations that I can use to solve for my unknowns?

 

[FOURe]

Bug6:

As far as I can see, units are not OK in the first equation -- there is no temperature multiplying first two terms in the equation.

I would suggest that you work with enthalpy values in your energy balance equations ...

Thanks,

Gordan

http://www.engineering-4e.com

 

[athomas236]

Remember also that you should use the NCV not GCV for heat balances.

I do not know any details about your incinerator but with boiler furnaces, radiation is the main form of heat transfer.

Regards,

athomas236

 

[athomas236]

When making a heat balance around a furnace I usually use a reference temperature of 25C since this is the basis of calorific values.

For the heat input I suggest the following:
m(sludge)*ncv(sludge)+m(diesel)*ncv(diesel)
+m(air)*cp(air)*(Air Temp(to furnace)-25)
+m(sludge)*cp(sludge)*(Sludge temp(to furnace)-25)
+m(diesel)*cp(diesel)*(Diesel temp(to furnace)-25)

For the heat output I suggest the following:
m(exhaust)*cp(exhaust)*(Temp(exhaust_out)-25)

This assumes that the incinerator is a refractory lined box which is basically at the same temperature as the gas in the incinerator which assuming a well stirred tank will be the same as the exhaust gas temperature.

Now there is only one unknown that can be solved by trial and error.

Please note that all cp's are mean values between 25C and the fluid temperature.

regards,

athomas236

 

[Bug6]

Thank you athomas for your help.