DIPOM : 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%   11,350 kJ/kg
Shells : 7% at Moisture     10%   18,840 kJ/kg
EFB    : 22% at Moisture   50%     8,160 kJ/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 100 DegC per kg of fuel of various calorific values at the following efficiencies.

• Latent Heat of Vaporization:

  Water requires 2,256 kJ/kg to convert from liquid to steam at its boiling point. 

• Fuel Calculation:

  If a fuel, like wood, has a calorific value of, say, 10,000 kJ/kg, and the boiler is 70% efficient, then it would require roughly 2,256 / (10,000 * 0.70) = 0.32 kg of wood to produce 1 kg of steam. 

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.

1kg of coal : 8kg of steam

1kg of gas : 17kg of steam

Fuel Available (kg/hr) Steam Evaporation (kg/hr)

10 tons FFB can produce 1.9 mt solid fuel with 7.6 mt steam as below:-

10 tons FFB/h 1,900 7,600
20 tons FFB/h 3,800 15,200
30 tons FFB/h 5,700 22,800
40 tons FFB/h 7,600 30,400
50 tons FFB/h 9,500 38,000
60 tons FFB/h 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

How to improve steam generation in palm oil mills?

To improve steam generation in a palm oil mill, focus on optimizing the steam cycle, enhancing combustion control, maintaining equipment, implementing energy recovery systems, and closely monitoring data. Specifically, this includes optimizing feedwater quality, recovering condensate, and potentially using steam accumulators. 

Detailed strategies:

1. 1. Optimize the Steam Cycle:

   • Feedwater Economizer: Installing a feedwater economizer can preheat the water before it enters the boiler, reducing the energy required to produce steam and improving overall efficiency. 
   • Blowdown Control: Reducing the blowdown rate of the boiler, potentially through an automatic blowdown control system, can minimize heat loss and improve steam quality. 
   • Condensate Recovery: Implementing systems to recover and reuse condensate (water from condensed steam) can significantly reduce water and energy consumption. 
   • Steam Accumulators: Using steam accumulators can help optimize steam supply and reduce the need for fresh water, particularly when production capacity is increased. 
2. 2. Enhance Combustion Control:

   • Fuel Optimization: Ensure proper fuel mixing and combustion conditions to maximize heat transfer efficiency and minimize fuel waste. 
   • Air/Fuel Ratio: Maintaining the correct air-to-fuel ratio is crucial for efficient combustion. Too much air can cool the flame, while too little can lead to incomplete combustion. 
3. 3. Maintain Equipment:

   • Clean Heat Exchangers: Regularly cleaning boiler heat exchange surfaces ensures maximum heat transfer from the burning fuel to the boiler water. 
   • Insulation: Proper insulation of steam pipes and equipment minimizes heat loss, improving steam pressure and reducing energy consumption. 
   • Regular Maintenance: Implement a regular maintenance schedule for all steam-related equipment to prevent leaks, corrosion, and other issues that can impact efficiency. 
4. 4. Implement Energy Recovery Systems:

   • Waste Heat Recovery: Explore opportunities to recover waste heat from sources like flue gas or exhaust steam from the sterilizer. 
   • Cogeneration: Consider cogeneration systems that can utilize waste heat to generate electricity, further improving energy efficiency. 
5. 5. Monitor and Analyze Data:

   • Real-time Monitoring: Install sensors and monitoring systems to track key parameters like steam pressure, temperature, and flow rate. 
   • Data Analysis: Analyze the collected data to identify areas for improvement and track the effectiveness of implemented changes. 

By focusing on these areas, palm oil mills can significantly improve steam generation efficiency, leading to reduced energy costs and increased overall plant efficiency.