I intend to calculate the thermal efficiency of my reactor in two scenarios.
(1) fully heated by LPG (propane+ butane fuel) continuously
(2) after heated by LPG, when pyrogas is released, pyrogas is used to sustain the temperature of the pyrolysis reactor.
Both situations have similar input and. output temperature.
Will Q=mc(delta theta) able to help? Still I fail to calculate using it.
Based on what you described in the question, you are asking how to calculate the hot-gas thermal efficiency (HGTE) of a pyrolyser. The HGTE is usually defined as the total LHV of the product vapour plus its sensible heat divided by the total LHV of the feed plus any auxiliary heat input, electric and/or sensible heat of any heating agent.
HGTE = [m1*LHV1 + m1*H1(T1)] / (m0*LHV0 + Q0) * 100% (1)
where m1 = Total mass flow of product gas/vapour (kg/h),
LHV1 = Lower heating value of product gas (kJ/kg),
H1 = Specific enthalpy of product gas (kJ/kg),
m0 = Feed rate (kg/h),
LHV0 = LHV of your feed (kJ/kg),
Q0 = Auxiliary heat input (kJ/h),
T1 = Temperature at pyrolyser outlet (°C).
Subscripts 0 and 1 denote input (feed) and output (product), respectively. Note that m1 may or may not be equal to m0 since you may use some inert gas in the feed.
The auxiliary heat input can be electric heating duty, total LHV of auxiliary fuel or recycled product, or recovered sensible heat.
Q0 = 3600*Qe + maf*LHVaf + mha*[Hha(Tin)- Hha(Tout)] (2)
Units in kJ, kw, kg and h. Subscripts e, af and ha stand for electric heating duty, auxiliary fuel and heating agent (e.g. a hot gas), respectively. Note that Tin is higher than the pyrolyser operating temperature, while Tout may not be the same as T1. If (Tin - Tout) is less than 300°C, you can use a mean heat capacity Cp of the heating agent.
Hha(Tin) - Hha(Tout) = Cp,ha*(Tin - Tout). (3)
For your Scenario 1 during start-up, Eq. (1) reduces to
HGTE = m1*H1(T1) / Q0 * 100%. (4)
For Scenario 2 during normal operation, use Eq. (1) directly to evaluate the thermal efficiency, but note that Q0 must be adjusted based on how much electric heating duty and auxiliary fuel is displaced by recycled product.
Hope this helps.
Xuantian Li: in equation (1), why is there T1? its existence made the equation not dimensionally consistent.
Meanwhile, does the T1 multiply with m1*H1 only? or {m1*LHV1 + m1*H1}
Hi Teo,
In Eq. (1), H(T) denotes H as a function of T, but not H*T, and so forth with other equations. All multiplications are written as *.
I agree with dr. Xuantian Li. This is a good equation to measure the thermal efficiency of the reactor, if you have detailed gas composition analysis of the product gas and reliable measure of the exiting temperature.
Xuantian Li & Pietro Bartocci:
May I know where can i read more on the equations above?
Any papers perhaps?
The answer is easy. the efficiency is a ratio of what we get effectively / what should be get.
Best regards!
There is still no conclusive answer as to how the thermal efficiency of a reactor can be calculated it seems.
Luka Zajec's calculations are as shown (in Slow pyrolysis in a rotary kiln reactor Optimization and experiment section 6.1.3 Analysis of drying test results)
Rasul and Jahirul's method is shown in section 6 Energy Consumption in Pyrolysis of Recent Developments in Biomass Pyrolysis for Bio-Fuel Production Its Potential for Commercial Applications
& there's no calculations/ equations to how "KBX" & "video" got their thermal efficiency more than 90%.
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