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Assessment of thermal efficiency of heat recovery coke making

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Abstract

The heat recovery stamp charge coke making process is quite complicated due to the evolved volatile matter during coking, is partially combusted in oven crown and sole flue in a controlled manner to provide heat for producing metallurgical coke. Therefore, the control and efficient utilization of heat in the oven crown, and sole flue is difficult, which directly affects the operational efficiency. Considering the complexity and importance of thermal efficiency, evolution of different gases, combustion of gasses in oven crown and sole flue, and heating process of coke oven has been studied. A nonlinear regression methodology was used to predict temperature profile of different depth of coal cake during the coking. It was observed that the predicted temperature profile is in good agreement with the actual temperature profile (R2 = 0.98) and is validated with the actual temperature profile of other ovens. A complete study is being done to calculate the material balance, heat balance, and heat losses. This gives an overall understanding of heat flow which affects the heat penetration into the coal cake. The study confirms that 60% heat was utilized during coking.

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Abbreviations

A/c:

Accumulation (kg)

a, b, … g:

Correlation coefficients

c:

Consumed (kg)

CC :

Mean specific heat of the dry coal (kg/kg °C)

\({\text{C}}_{\text{K}}\) :

Mean specific heat of coke (kcal/kg °C)

\({\text{C}}_{\text{p}}\) :

Mean specific heat of the dry air (kcal/m3 °C)

\({\text{c}}_{\text{p}}\) :

Specific heat of water vapour (kcal/m3 °C)

CW :

Mean specific heat of the moisture (kg/kg °C)

\({\text{C}}^{{0,{\text{t}}}}\) :

Mean specific heat of gas between 0 and t °C at constant pressure (kcal/m3 °C)

\({\text{C}}_{\text{p}}^{{0,{\text{t}}}}\) :

Mean specific heat of coke oven gas between 0 and t °C (kcal/m3 °C)

F:

Area of exposed surface (m2)

G:

Generation (kg)

I/p:

Input (kg)

K:

Thermal conductivity (Wm−1K−1)

K1, K2, … Kn:

Thermal conductivity of each material (Wm−1K−1)

Eeffective :

Effective thermal conductivity (Wm−1K−1)

L:

M3 of dry air supplied for burning 1 m3 of gas

L1, L2, … Ln:

Thickness of each material (mm)

O/p:

Output (kg)

q:

Total thermal heat input (kcal/t)

\({\text{q}}_{1}\) :

Heating effect of coke oven gas (kcal/t)

\({\text{q}}_{2}\) :

Sensible heat of the coke oven gas (kcal/t)

\({\text{q}}_{3}\) :

Sensible heat of the air supplied for combustion (kcal/t)

\({\text{q}}_{4}\) :

Sensible heat of moist coal blend (kcal/t)

\({\text{q}}_{1}^{\prime}\) :

Sensible heat of coke (kcal/t)

\({\text{q}}_{2}^{ '}\) :

Sensible heat of flue gas at the moment of leaving chamber (kcal/t)

\({\text{q}}_{3}^{ '}\) :

Heat of by-products viz., coal tar, NH3 and H2S (kcal/t)

\({\text{q}}_{4}^{ '}\) :

Total heat of condensed steam (kcal/t)

\({\text{q}}_{5}^{ '}\) :

Sensible heat of the waste gases (kcal/t)

\({\text{q}}_{6}^{ '}\) :

Potential heat of waste gases (kcal/t)

\({\text{q}}_{7}^{ '}\) :

Heat losses to the surroundings (kcal/t)

\(\frac{\text{Q}}{\text{A}}\) :

Heat loss per unit area (kcal/t/m2)

\({\text{Q}}_{\text{nm}}\) :

Net heating value of the moist gas (kcal/m3)

t:

Temperature of coke oven gas at the movement of leaving the chamber (°C)

t0 :

Ambient temperature (°C)

tb :

Boiling point temperature of the water (°C)

t1 :

Temperature of the surface (°C)

t2 :

Temperature of surroundings (°C)

tC :

Temperature of the coke when ready (°C)

th :

Coking time (hr)

Ths :

Temperature of the hotter surface (°C)

Tcs :

Temperature of the cooler surface (°C)

TN :

Temperature of coal cake at a particular time (°C)

TN−1 :

Temperature of adjacent layers (°C)

\({\text{V}}_{\text{X}}\) :

Amount of heating gas per ton of coal (Nm3/ton)

\({\text{V}}_{\text{g}}\) :

Amount of dry coke oven gas (Nm3/ton)

W:

M3 of water vapour in 1 m3 of dry air

\({\text{W}}_{\text{CT}}\) :

Moist content of the coal blend per ton of moist coal (kg/ton)

\({\text{Y}}_{\text{CT}}\) :

Yield of dry coal per ton of moist coal (kg/ton)

\({\text{Y}}_{\text{KT}}\) :

Yield of coke (kg/ton of coal)

α0 :

Overall heat transfer coefficient by radiation and convection (kcals/m2 hr °C)

\({\eta u}{\text{f}}\) :

Underfiring efficiency (%)

\(\upeta \uptau {\text{C}}\) :

Thermal efficiency (%)

\(\uprho\) :

Density of coal particle (kg/m3)

∆x:

Position is a function of depth of coal cake (mm)

α:

Thermal diffusivity

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Authors and Affiliations

  1. Coal and Coke Making Research, Research & Development, Tata Steel Ltd., Jamshedpur, 831001, Jharkhand, India

    H. P. Tiwari & S. K. Sriramoju

  2. Department of Chemical Engineering, ISM, Dhanbad, India

    V. K. Saxena

  3. Tata Steel Ltd., Jamshedpur, 831001, Jharkhand, India

    S. K. Haldar

Authors
  1. H. P. Tiwari
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  2. V. K. Saxena
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  3. S. K. Haldar
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  4. S. K. Sriramoju
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Correspondence to H. P. Tiwari.

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Tiwari, H.P., Saxena, V.K., Haldar, S.K. et al. Assessment of thermal efficiency of heat recovery coke making. Heat Mass Transfer 53, 2517–2529 (2017). https://doi.org/10.1007/s00231-017-2003-x

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