The Qianjiaying mine and washery complex is some 200 km east of Beijing. Regarded as one of China's efficient mining operations, it is a business unit of the 127-year-old Kailuan Group, a diversified industrial conglomerate and top-ten Chinese coal miner.
The Group’s proven coal reserves are in the vicinity of 7.1 billion tons, the bulk of which will go to domestic steelmaking and power generation.
The washery has ten float tanks that, under the washery’s two-stage processing program, were run as five banks of two. For some time washery management had been keen to convert to the more efficient single-stage processing system, but the existing collector medium (diesel) was unable to float the coarse coal in the single-stage format.
According to Liu Taishun, director of the Qianjiaying washery, the management team had made a number of production improvements including improvements in the coarse coal system and the introduction of a heavy medium (HM) separation process and were keen to extend those improvements to the fine coal circuit.
The HM upgrade had markedly increased the yield of coarse coal, and new production levels were being achieved. However, according to Li Jianguang, director of the CPP department and technical officer of CPP technology in the Kualin Group, the yield in the flotation circuit was still low due to the characteristics of the feed.
With the focus now firmly on increasing the yield from the singlestage float circuit, research was conducted regarding the various options available, including use of chemical compounds. That research put washery management in contact with Nalco ’s Beijing office.
The outcome of those initial discussions was a site trial of Nalco’s coal flotation program.
An analysis of the coking coal processed at the Qianjiaying washery revealed that ash content in the raw feed was in the 38-41% range, while feed to the fine coal float circuit was running between 18%-30% ash.
The coal was considered hard to float. Nalco’s response was to use its NALFLOTE 9836 Collector for trial. Described as a highly selective reagent, NALFLOTE 9836 is a blend of active organic compounds and surface-active agents that make it appropriate for use over a wide particle size range and particularly effective for coarse coal.
The trial started in July 2005 and ran for five weeks with plant feed at 950 t/h allowing for a detailed analysis of the Nalco collector’s impact on the varying ash contents of the float circuit feed. It also gave an indication of impacts on washery operations downstream of the float cells.
Various coal types existed during the trial, including a hard-to-float coal not previously experienced. Even with the presence of hard-to-float coal, the collector still exhibited good selectivity and continued to control-clean coal ash.
Throughout the trial, collector amounts were varied in an effort to find optimum levels for the coal types processed. Ultimately a number of dose rates were determined to account for the diversity of ash content in the feedstock.
Along with an almost immediate and positive impact on yield, the trial also confirmed that NALFLOTE 9836 could successfully float the coarse, low-ash coal.
The product also proved to be suitable for a range of coal types and effective in lowering the product ash when used with hard-to-float coal.
At the conclusion of the trial, flotation yield had increased by more than 9%. For Qianjiaying, this meant an additional 7,000 tons of clean, saleable coal per month.
“The program is performing above expectations,” said Liu Taishun, who closely monitored and supported the trial with Li Jianmin, vice president of the Kualin Group; Huo Zhongfeng, president of the Qianjiaying coal mine; Cui Fenglu, vice president of Qianjiaying coal mine; and Li Jianguang.
Also observing and monitoring the trial of the new collector was Tong Shunzeng, vice director of Qianjiaying washery, and the chief engineer, Zhutianwei.
Liu Taishun added that the program had been successfully integrated into the Qianjiaying washery due to the strong cooperation between the washery management team and Nalco personnel.
“The effort invested in this project has delivered excellent outcomes,” he said.
Implementation of the full program has also delivered a range of flow-on benefits at the Qianjiaying washery.
The inherent antifoam properties of the NALFLOTE 9836 have allowed for higher dosages of frother to increase yield beyond the original target.
After just two days of using the new collector, foam content in the tailings thickeners dropped significantly below the levels experienced when diesel was used as a collector reagent.
The cost per ton yield has also been lowered with the reduction in dose of collector required under normal operating conditions, and air quality within the vicinity of the float circuit has also been improved with the pungent diesel/kerosene fumes replaced by the organic odour of the NALFLOTE 9836.
The Qianjiaying washery is one of six such facilities operated by the Kailuan Group. The results achieved at Qianjiaying could be used as a basis for trials at their other coking coal washeries.