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Frequently Asked Questions

1. 3% efficiency… it’s not a lot!

Mr Sanches, a Portuguese industrialist, has done his research and needs a 5MW natural gas steam boiler. He thinks that it will operate at nominal power for 50% of the time. Babcock Wanson offers him a solution with 95% efficiency, but Mr Sanches is unsure, because this offer is €10K more expensive than that of a competitor offering a boiler with 92% efficiency.

From the economic point of view, what would you advise Mr Sanches? And from an environmental point of view, how many trees does it take to absorb the CO2 emissions differential between the two solutions?


Boiler Output

5 000 











Burner Output

5 435

 5 263


 (= Boiler Output / Efficiency)


Price of the KWh Gas





Annual Operating Time

 4 380


(= 50 % x 365 j x 24 h) 


Annual Cost

 714 130,43 €

 691 578,95 €


(= Burner Output x Price of gas x Operating time) 


 Annual Cost Difference

22 551,49 € 





Conclusion: The real added value of Babcock Wanson boiler is amortised in less than 6 months.


CO2 equivalent CO2 per kWh gas



 (Source: ADEME)


Average absorbed CO2 amount by a tree per year (kg)



(Source: TreeCanada)

This figure varies regarding the tree’s species and age


Amount of CO2 emissions produced per year

4 903 696

4 748 842


(=Burner output x Operating time x CO2 equivalent)


Difference of CO2 emissions per year (kg)

 154 854




The relevant number of trees to absorb the difference of CO2 emissions *

22 122


 (= Difference of CO2 / Absorbed CO2 amount)


 * The CO2 absorption is only temporary because it depends on the tree life and the stored CO2 will be released when it’s dead. Thus, a tree will released tomorrow the CO2 absorbed today. That’s why it’s important to minimize the CO2 or other pollutants emissions.




A customer wants us to treat their steam boiler water which is fed from a tank at 80°C (i.e. 2.8mg of O2 per litre). For the year, the steam production is 17000 tonnes, the condensate return volume is 8500 m3 and the blowdown purge represents 2000 m3/year. Our product W9400L contains sulphites that can degrade the oxygen (40g of product to degrade 1g of oxygen).

=> What annual quantity of W9400L will our customer need to prevent corrosion problems?

Solution :

Boiler feed water = steam production + purge

Boiler feed water = 17000 + 2000 m3

(The back flow of condensate has to be retreated)


Product dosage (neglecting the residual sulphite to be present in the boiler)

If 40 g of the product is needed to degrade 1g of oxygen

2.8 x 40 = 112 g/m3


The annual product quantity will be

19000 x 112 = 2 128 Kg  

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