Decoking is decarbonisation, but it refers more specifically to removing the "soot" i.e solid carbon / coke, from the walls of the burner using a mixture of air and steam. I think that is what the text is referring to because this is an occasional procedure ("Cuando se requiera....") whereas reducing CO2 gas emissions would be a constant process.

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Note added at 1 hr (2013-06-12 17:15:31 GMT)
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Optimization of the Decoking Procedure of an Ethane Cracker with a ...
pubs.acs.org/doi/pdfplus/10.1021/ie060381a
The furnace is heated with 128 burners positioned in. 8 rows of 8 burners in the front and the rear wall of the furnace. During the standard decoking operation, ...

Patent US8152993 - Ethylene furnace radiant coil decoking method ...
www.google.co.uk/patents/US8152993‎
Apr 10, 2012 – A method for decoking the radiant coils in an ethylene furnace comprising the steps of: (a) providing a flow of steam and firing burners in the ...

http://www.red-bag.com/jcms/design-guides/351-bn-dg-c01g-pla...
6.1 Decoking
(See below figure 12)
The internal cleaning of tubes and fittings may be accomplished by several methods. One is to circulate gas oil through the coil after the heater has been shutdown but before the coils are steamed and waterwashed and prior to the opening and start of inspection work.

This method is effective if deposits in the coil are such that they will be softened or dissolved by gas oil. When tubes are coked or contain hard deposit, other methods may be used, such as steam air decoking and mechanical cleaning for coke deposits and chemical cleaning for salt deposits. Chemical cleaning and steam air decoking are preferable as they tend to clean the tube to bare metal. The chemical cleaning process requires circulation of an inhibited acid through the coil until all deposits have been softened and removed. This is usually followed by water washing to flush all deposits from the coil. Steam air decoking process consists of the use steam, the coil. Steam air decoking process consists of the use of steam, air and heat to remove the coke. The mechanics of decoking are:
a. Shrinking and cracking the coke loose by heating tubes from outside while steam blows coke from the coil.
b. Chemical reaction of hot coke with steam.
c. Chemical reaction of coke and oxygen in air.
Steam and air services are permanently connected to the heater. The heater outlet line incorporates a swing elbow which, during the decoking operation, is disconnected from the outlet line and connected to the decoking header. Care must be taken to allow sufficient access and platforming when the swing elbows are changed over. Coke is carried by this header to the drum or sump.
In some instances it may requested by the Process Department or Client that the decoking manifold is connected to allow for reverse flow during the decoking.