Advantagesand Issues –CO2 fromnormal combustion (using air), is present as a dilute fluid in the flue gasstream, which turns out to be an expensive method to capture carbon dioxidefrom the nitrogen rich mixture through amine absorption. CO2 capture can beaccomplished by combusting fuel with oxygen to get a concentrated co2 streamthat can be easily sequestered. Theprocess is a thermally efficient process because there is little or no nitrogento heat. Besides NOx emissions are drastically decreased.Despite,oxygen extraction or purchase is expensive, oxyfuel combustion can be proven tobe cost efficient since there is no need for additional furnace due to the highenergy efficiency of the process.
Anotheradvantage is its potential to be retrofitted to existing plants, also it couldbe allowed in a new plant for retrofit at a later stage, very environmentallyfriendly due to the low NOx emissions and sequestration of CO2 for transportationand storage. Onthe other hand, the disadvantages of the technology are also mentioned in thisparagraph. For instance, there is a lack of information as there are nofull-scale plant using oxyfuel combustion but pilot scale experiments.
Anotherpoint not in favour, is the cost for additional units for the desulphurisationprocess. It is important to mention that air separation is an energy intensive stagewithin the process for this reason the overall efficiency is less compared tothe one currently used pulverised fuel technology.BestFit – It can beconsidered as a cost-efficient solution when clients are willing to increaseperformance or reduce Nitrogen oxides emissions. It may be the best fit forplants where higher production is desired (30%) as well as reducing the cost offuels for up to 15%. Resulting in doubled profit margin and shorter paybacktimes, however if reducing fuel costs is the only target, this technology mightnot be appropriate. CriticalReview – Experiments carried out using this technologyhave encountered some design issues, they can be categorised according to theirorigin.
Thefirst, is about design problems related to heat transfer. These problems arecaused due to gas thermal capacity (pure oxygen is combusted) and gas radiativequalities, the latter is caused by the increased concentration of COx and watervapour in the furnace which will cause the concentration of triatomic moleculesto drastically increase in the flue gas thus modifying the emissivity of thegas.Thesecond issue is related to the emissions, clearly the amount of NOx emissionshas drastically decreased, however the amount of sulphur remains unchanged. Inthe final stage, compression and liquefaction of CO2 will generate anon-condensable stream of components that could leak from air, since they getrecirculated these could build up, for this reason this issue needs to beaddressed in order to meet the equipment regulations along with environmentrequirements.
Thethird issue is related to ash accumulation that if recirculated could increasethe combustion temperature and hence modifying the boiler operability, a lastissue is related to ignition and flame strength, this type of stability-relatedissue is supported by experimental data from the pilot plants.Toaddress these problems accurately, more funding should be allowed for R&Dnow because corporations do not measure the effect of their conventional plantson the environment, it may be late when action is taken. The solution from ageneral point of view is to increase research so the process is finallyimplemented in a full-scale plant and not just stay in literature as a ‘nearzero technology’ that was only experimental.