Technical service and assistance is fast becoming more important and increased emphasis is being placed on environmental issues. Pretorius Energy utilises the services of various technical specialist who can provide the following services:

Regular technical visits to Pretorius Energy customers

Assistance with coal quality queries and general combustion problems

Boiler settings, efficiency testing and operational procedures

Sampling of problematic coal and submission to independent laboratories for analyses.

Noko Analytical Services

Inspectorate M&L

MAK Analytical

Stack emission tests and other environmental requirements etc.

Water and Fire side treatment

Boiler Maintenance

Boiler pressure test and 3 yearly inspections

Boiler operator training

Technical Questions /Frequently Asked Questions

The fire in the boiler keeps running away. Why?

Cold ignition arch Low volatiles in coal Coal sizing too big Stoker speed too fast To much air

The chain grate is too hot – Why?
Fuel bed too thick, resulting in insufficient cooling by FD fan
Uneven air destitution

The boiler pressure stays low – Why?
Increased steam requirement too quickly
Fuel bed is too thin
Stoker speed too slow
Coal Quality

 Consistent dark chimney smoke and high CO2 reading – Why?
Coal bed is too thick
Incorrect air/fuel ratio
Dirty fire tubes / Grid arresters
Excessive high volatile content in coal

What is the desired carbon dioxide (CO2) percentage?
The CO2 content gives an indication of the combustion efficiency in the furnace and should be about 13%. A low CO2 reading is an indication that volatiles are not completely burnt

Calorific Values (CV)
Units:
kcal/kg Kilocalories per kilogram
MJ/kg* Megajoules per kilogram
Btu/lb British Thermal Units per pound
* 1 MJ/kg = 1 Gigajoule/tonne (GJ/t)

Gross & Net Calorific Values
Gross CV or higher heating value (HHV) is the CV under laboratory conditions.
Net CV or lower heating value (LHV) is the useful calorific value in boiler plant. The difference is essentially the latent heat of the water vapour produced

Conversions Units
From kcal/kg to MJ/kg multiply by 0.004187
From kcal/kg to Btu/lb multiply by 1.800
From MJ/kg to kcal/kg multiply MJ/kg by 238.8
From MJ/kg to Btu/lb multiply MJ/kg by 429.9
From Btu/lb to kcal/kg multiply Btu/lb by 0.5556
From Btu/lb to MJ/kg multiply Btu/lb by 0.002326
Conversions Gross/Net (per ISO, for As Received figures)
kcal/kg: Net CV = Gross CV 50.6H 5.85M 0.191O
MJ/kg: Net CV = Gross CV 0.212H 0.0245M 0.0008O
Btu/lb: Net CV = Gross CV 91.2H 10.5M 0.34O
where M is % Moisture, H is % Hydrogen, O is % Oxygen (from ultimate analysis*, also As Received).
Ultimate analysis determines the amount of carbon, hydrogen, oxygen, nitrogen and sulphur.
For typical bituminous coal with 10% M and 25% Volatile Matter, the differences between gross and net calorific values are approximately as follows

260 kcal/kg

1.09 MJ/kg

470 Btu/lb

Power Generation
1 MWh = 3600 MJ
1 MW = 1 MJ/s
1 MW (thermal power) [MWth] = approx 1000 kg steam/hour
1 MW (electrical power) [MWe] = approx MWth / 3
A 600 MWe coal-fired power station operating at 38% efficiency and 75% overall availability will consume approximately:
Bituminous coal (CV 6000 kcal/kg NAR*): 1.5 Mt/annum
Brown coal (CV 2250 kcal/kg NAR*): 4.0 Mt/annum