Fuel Steam Balance

1. Basic Requirement

Crop must be processed at a certain hourly throughput rate to give sufficient quantity of fuel in the form of palm fibres and palm shells for burning in the steam generating boilers to produce sufficient quantity of high pressure steam which will, in turn, provide the necessary motive power as well as the necessary process steam needed to run the Mill economically.

2. Crop Projection

• Giving information about the area from which the FFB must be processed.
• The type of planting material and age of planting.
• Expected yield per acre from maturity to peak production at 9-10 years from planting.

3. Throughput Table
Having established a crop projection and assuming 12% of the annual crop in any peak month, it is possible to plan a factory throughput based upon one or two shifts operation up to 20 hours/day as indicated in the following table.

4. Conversion Of Crop To Fuel

Fuel produced per hour is related to :
(i) hourly FFB throughput rate
(ii) type of planting material - ratio of fuel to FFB
(iii) losses in palm fibres/shells/EFB
Ratio of total fuel available as a % of FFB is as follows :
Fuel Ratio to FFB by Weight Net calorific value
Fibres : 12% at Moisture 38% 11,350kJ/kg
Shells : 7% at Moisture 10% 18,840kJ/kg
EFB : 22% at Moisture 50% 8,160kJ/kg
A completely mixed fibre/shells fuel can give a net energy value of about 14,100 kJ/kg.

5. Conversion Of Fuel To Steam

Kg of water evaporated from and at 1000C per kg of fuel of various calorific values at the following efficiencies.

The thermal efficiency of a boiler naturally depends on the type of boiler installed, cleanliness of the fire or water tubes and general efficiency of operation. It is however, safe to assume a thermal efficiency of about 70% which at a fuel of 14,000 kJ/kg will give about 4.0 kg of steam/kg of fuel. Total steam which can be generated from the fuel available is shown hereunder.
Fuel Available (kg/hr) Steam Evaporation (kg/hr)
10 tons FFB/h 1,900 7,600
20 “ “ 3,800 15,200
30 “ “ 5,700 22,800
40 “ “ 7,600 30,400
50 “ “ 9,500 38,000
60 “ “ 11,400 45,600
From above table it appears that the fuel available at a throughput of 30 tons of FFB/h should be sufficient to evaporate about 22,800 kg of steam. It should therefore be possible to establish the fuel/steam balance by installing a
22 T/hr boiler.

6. Power Requirements In The Mill

Some of the actual values obtained :
Mill Size Power Consumption
10 T FFB/hr 28 kWh/T
20 T FFB/hr 20 kWh/T
30 T FFB/hr 16-17 kWh/T
40 T FFB/hr 18-19 kWh/T
50 T FFB/hr 18-19 kWh/T
60 T FFB/hr 19-20 kWh/T
These mills supply steam power for processing as well as domestic load. This does not include additional equipment such as extended effluent treatment plant, decanters and EFB presses.

7. Process Steam Requirement In The Mill

(As a guide only - obviously the steam consumption depends on the way we run the Mill and how well the steam system & steam traps are maintained)
L.P. Steam
1. Sterilisation single peak 100 kg/T FFB
double peak 200 kg/T FFB
triple peak 270 kg/T FFB
2. Other Process Units : 250 kg/T FFB

H.P. Steam
Deaerators &
Steam Feed Pumps : 125 kg/T FFB
depending on whether reciprocating or turbine
driven steam feed pumps are used.
TOTAL single peak 475 kg/T FFB
==== double peak 575 kg/T FFB
triple peak 645 kg/T FFB
Rule of thumb figures for process steam requirements :
0.4 - 0.5 T steam/T FFB on average