research team from the Gas Processing Center (GPC) at Qatar University
College of Engineering (QU-CENG) has developed a combined approach for
carbon and high salinity water (reject brine) management.
Led by GPC Qafco chair Prof Muftah El-Naas, the team developed and tested a modified Solvay process that does not involve the use of ammonia. Reject brine was mixed with 1% to 2% of calcium oxide to raise the water pH to above 10 and then contacted with carbon dioxide (CO2)-containing gases.
The CO2 reacts with sodium chloride and calcium hydroxide to form soluble calcium chloride and insoluble sodium bicarbonate. This process has the dual benefits of capturing CO2 and storing it in solid sodium bicarbonate and, at the same time, reducing the salinity of the reject brine.
In addition to mitigating the negative impact of CO2 emissions, the new process can significantly reduce the salinity of reject brine, so that it can be used for irrigation purposes or enhanced oil recovery. An important part of the new process is a novel reactor system that was especially developed to facilitate the direct contact between the CO2 gas and the high salinity brine.
Prof El-Naas noted that seawater desalination is a major source of potable water in Qatar and most countries in the region.
He said: “It is estimated that the Gulf countries contribute in about 44% of the world production of desalinated water, amounting to about 37mn cubic metres a day. A similar amount of highly concentrated reject brine is also produced daily. The management of such large quantities of reject brine represents major economic and environmental challenges to most desalination plants, especially those involving thermal desalination. Conventional management methods such as disposal through deep well injection, land disposal and evaporation ponds have proved to be ineffective and often lead to negative impacts on the environment.”
He noted that CO2 emission is yet another environmental concern that is considered a major contributor to global warming.
CO2 is believed to have the greatest adverse impact on the observed greenhouse effect, he said, adding: “CO2 emissions come predominantly from the combustion of fossil fuels in power generation, industrial facilities, buildings and transportation. A different approach for carbon capture and storage has been proposed as a possible, reliable and environmentally friendly option for the containment of CO2 emissions. It involves the reaction of carbon dioxide with high salinity water such as desalination reject brine or produced water.”
“It is worth noting here that this new system has the potential to be used for several industrial applications, such as water desalination, reject brine management, and produced water treatment as well as natural gas treatment processes such as gas sweetening. Therefore, several Qatari industries such as Kahramaa, Qatar Petroleum and Qatargas will be interested in developing the technology associated with the process or the reactor system.”
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