For centuries, the three main gas emissions from steel mills, namely the gases from the blast furnaces, the converters and the coke ovens, have been difficult to recover and re-use. Among them, the volume of blast furnace gas emitted is the highest.
This by-product gas is considered the secondary energy of the steel mill and should theoretically have a high economic value – and be recovered and re-used.
Various research institutes in China have put substantial efforts into this and Beijing Peking University Pioneer Technology Co. Ltd (PKU Pioneer), a direct subsidiary of the Peking University, has recently achieved a breakthrough.
PKU Pioneer completed a project to tackle this technical issue, supplying a set of CO recovery equipment to Hengyang Valin Steel Tube Co. Ltd (Henggang) to recover the carbon monoxide from the blast furnace gas.
The gas is the most difficult to treat because it contains a nitrogen content of up to 50% or higher, and the boiling points of carbon monoxide (CO) and nitrogen are similar – so separating them effectively is a hard nut to crack for the steel industry globally. The high nitrogen content also leads to a low calorific value (about 3,500kJ/Nm3), resulting in a low combustion efficiency.
Usually it is just discharged to the atmosphere, but if a solution to this technical problem could be found, the steel industry could make use of the CO-rich gas for efficient combustion or use it as the reduction gas in the blast furnace. Carbon emissions could be also reduced substantially.
Furthermore, the CO in the blast furnace gas could be enriched to more than 99% and be used as the raw material of synthetic chemical products, further improving the added value of the gas and creating considerable monetary benefits for the enterprise.
The equipment from PKU Pioneer recovers 17,500 Nm3/h of CO products (purity higher than 70%) from 6,7000 Nm3/h of blast furnace gas. The company claims in its announcement that it is the world’s first industrial scale carbon monoxide recovery equipment for such applications. The equipment was commissioned for Henggang in June last year (2013) and so far has met or exceeded all performance criteria.
Second-phase signed off
Henggang is a subsidiary of Hunan Valin Iron & Steel Group Co., Ltd and one of the largest seamless steel tube and pipe manufacturers in the world, and the second-biggest seamless steel tube and pipe producer in China.
Henggang is located in Hengyang city of Hunan province and is at the end of the natural gas pipeline network. The company used to inject natural gas into the blast furnace gas to improve the calorific value so that it could be used in the heating furnace of the rolling mill. It now directly injects the CO-product from the recovery equipment into the heating furnace and increases the calorific value to 8,800kJ/Nm3 and can substitute 3382×104Nm3 of natural gas (38,000 tonnes of standard coal equivalent), which is around a quarter of the original natural gas consumption – relieving Henggang in its demand of natural gas.
Furthermore, since the nitrogen content in the purified CO has decreased, the volume of flue gas as compared with the original case of injecting natural gas has also decreased substantially; improving the radiation heat exchange effect, significantly lifting the energy saving benefits, and contributing a monetary saving of RMB 25m.
With such a satisfactory performance, Henggang has already signed a contract with PKU Pioneer for the second phase of the project.
Besides the equipment for the blast furnace, PKU Pioneer has also supplied the first equipment in China for recovery and purification of carbon monoxide from calcium carbide furnace exhaust to Xinjiang Tianye (Group) Co., Ltd (a leading enterprise in the calcium carbide industry) and has been successfully used in MEG synthesis.