General information Useful calculation data
7
Steam pressure bar g
Feedwater temperature °C
Mathematical operation
Units kJ/kg
Heat input required (see table 1)
x =
1000
kg kJ
Total heat input
kJ/kg coal or oil kJ/kWh gas kJ/kg coal or oil kWh gas
÷
Calorific value of fuel (see table 2)
=
Net fuel needed
85% x 1.18 80% x 1.25 75% x 1.34 70% x 1.43
x
Boiler efficiency
kJ/kg coal or oil kWh gas
=
Actual fuel needed
COAL
OIL
GAS
S.G Heavy 9.7 Medium 9.5 Light 9.35
Mathematical operation
Mathematical operation
Mathematical operation
÷ = x
1000 kg/tonne
÷ = x
x
pkWh
tonne
litre
£/tonne £/1000 kg steam
£/litre
£/1000 kg steam
÷ 100 =
£/1000 kg steam
=
=
Table 1 Heat input in Kilojoules (kJ) required to raise one kilogram (kg) of steam. Boiler pressure bar g Feedwater temperature °C 10 20 30 40 50 60 70 80 90
100
110
1
2665 2623 2581 2539 2497 2455 2413
2371 2329 2287 2245
5 2715 2673 2631 2589 2548 2506 2464 2421 2381 2338 2295 6 2722 2680 2638 2596 2555 2513 2471 2428 2388 2345 2302 7 2727 2685 2643 2601 2560 2518 2476 2433 2393 2350 2307 10 2740 2697 2655 2613 2573 2531 2489 2445 2406 2363 2319 12 2746 2704 2662 2620 2578 2536 2494 2452 2410 2368 2326 15 2752 2710 2668 2626 2584 2542 2500 2458 2416 2374 2332 17 2755 2713 2671 2629 2587 2545 2503 2461 2419 2377 2335 20 2759 2717 2675 2633 2591 2549 2507 2465 2423 2381 2339 25 2762 2720 2678 2636 2594 2552 2510 2468 2426 2384 2342
7.5 3
Table 2 Calorific value of various fuels (approximate values)
TYPE
CALORIFIC VALUE (kJ/kg)
ANTHRACITE
32,500 30,000 28,000 21,000
COAL
GOOD BITUMINOUS COAL
GOOD AVERAGE INDUSTRIAL COAL POOR AVERAGE INDUSTRIAL COAL
GRADE
VISCOSITY
SPECIFIC GRAVITY
CALORIFIC VALUE (kJ/kg)
cSt
RED. 1 SECS
GAS OIL
4
35
0.835 0.935
45,600 43,500 43,000 42,500
OIL
LIGHT
50
210 950
MEDIUM HEAVY
230 900
0.95 0.97
3500
GAS
3,600 kJ/kWh
AI-GAB-03 AB Issue 4
Page 3 of 3
The Cost of Steam - Metric
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