Tangshan steelworks overcomes water shortages by recycling mine wastewater
China's Tangshan Iron & Steel Group Co. Ltd (TISCO) had to find a greater supply of clean water for boiler makeup and steel plate cooling without violating new national water consumption ratio laws. Membrane technology from Koch Membrane Systems -- including KMS Magnum high rejection spiral wound elements and TARGA hollow fiber pressure cartridges -- allowed it to treat wastewater from an old coal mine and support increased capacity without consuming scarce fresh water resources in the region...
By John McArdle and Ruming Pang
For 60 years, the Tangshan Iron & Steel Group Co., Ltd. (TISCO) in the Hebei province of northeastern China has benefited from an abundance of nearby iron ore and coal mines, proximity to customers in the adjacent industrial centers of Beijing and Tiajin provinces, and access to international markets via the Yellow Sea.
With 40,000 employees, TISCO is the sixth largest metallurgical enterprise in China, producing seven million tons of iron, steel and steel products in 2004. Aggressive plans are in place to increase production to 13 million tons by 2007. That includes expanding its hot and cold rolling capacity to add value to its products and increase profit margins.
Although there's no shortage of coal and iron, the scarcity of one critical natural resource has presented a significant challenge to TISCO's growth plans -- the lack of clean water for boiler makeup and steel plate cooling.
The supply of water for industrial use is limited due to the national shortage of freshwater. More than 700 million people, which is over half the country's population, are without access to drinking water that meets minimum World Health Organization (WHO) standards. The situation is particularly serious in the north, which contains 50% of the population and 65% of the farmland, but only 20% of the country's water resources. The residents of Hebei have historically relied on the overflowing waters of the Yellow River and its tributaries, but in the past decade, the region has been plagued by long periods of drought, making it even more challenging to obtain fresh water.
As a solution to the region's water scarcity dilemma, the Chinese government has promulgated regulations to conserve as much water as possible for residential and agricultural use, and to limit industrial water pollution. Water conservation and sustainable development was a central focus of the tenth Five-Year Plan of the People's Republic of China. For example, Chapter 5 of the 2002 Water Law required all industries to extensively reuse water and increase water recovery, especially during new construction or plant upgrades. For the iron and steel industry, the regulations specify water intake lower than 16 cubic meters per ton (m3/ton) of product and water reuse ratio higher than 90%.
In January 2005, the Chinese government imposed a new water consumption ratio on seven industries. Steel, power, petroleum and chemical, textile, papermaking, brewing and alcohol companies could now be charged a fee for any consumption of water over the allocated amount. If the situation is not rectified within a specified timeframe, the offending enterprises will lose access to the water supplies.
Water from Abandoned Coal Mines
In order to gain approval for its expansion plans, TISCO needed a plan that minimized its usage of scarce municipal water supplies. The solution was to once again take advantage of the locally available resources and exploit an alternative water source -- the wastewater in an abandoned coal mine less than 5 kilometers from the plant. The plentiful supply is a mixture of rainwater, groundwater and leached chemicals.
This mine contained a plentiful and reliable supply of water, but unfortunately, the water was difficult to treat because of its high quantity of suspended particles and dissolved solids, which were made up primarily of coal powder.
To successfully utilize water from this coal mine, TISCO looked to a bordering province that had recently dealt with the same problem. "We found a water treatment solution that had been successful on similar water in another abandoned mine," said Wanlin Tian, Manager of the new water treatment plant at TISCO. "At the Datong Mine, in the bordering province of Shanxi, they have been converting mine water into high quality drinking water for the people of the region since June 2003. We used the Datong system as a model for the new Tangshan Steel Works water treatment plant."
Membrane Water Treatment Plant
The core of the treatment plants, at both the Datong Mine and the new TISCO plant, is reverse osmosis (RO) membranes from Koch Membrane Systems, Inc., (KMS) of Wilmington, Massachusetts, in the United States. The two plants also utilize KMS ultrafiltration (UF) membranes to pretreat the water prior to RO. The new TISCO plant was supplied by Huadian Water Treatment Technology and Engineering Co. Ltd. and was commissioned in July of 2004.
The first stage of treatment at TISCO is conventional pretreatment involving coagulation, flocculation and sedimentation. After the pretreatment, the total suspended solids are about 20-100 mg/L and the turbidity is approximately 5 NTU. The total dissolved solids are in the range of 5-600 mg/L.
The second stage of treatment is ultrafiltration, which is performed by 46 KMS 8" (213mm) diameter TARGA® UF cartridges in three parallel trains, with a total capacity of 680 m3/hr. These hollow fiber cartridges have proprietary polysulfone membrane chemistry with a nominal molecular weight cut-off of 100,000 daltons. The high chlorine resistance (up to 200 parts per million at 10.5 pH) and pH tolerance (from 1.5 to 13) make these hollow fiber cartridges relatively easy to clean. The UF system removes suspended solids and turbidity to ensure excellent water quality for the RO feed.
The third stage is the reverse osmosis system. Three trains have a total capacity of 500 m3/hr. Each train has 108 Fluid Systems® TFC®-HR Magnum® spiral wound RO elements manufactured by KMS. The thin film composite membrane is made of a proprietary polyamide that provides high rejection at a relatively low RO operating pressure. The 60" (1,524 mm) long Magnum elements were selected over 40" (1,016 mm) long elements to minimize the number of components in the system. An additional stage of treatment, using ion exchange, is employed for polishing of water destined for use as boiler make-up water.
A Model for Sustainable Development
"The water treatment system has been a great success," according to water plant manager Wanlin Tian. "We are very proud that we implemented a creative solution to meet our water needs. We support the increased capacity of the Tangshan Steel Works, which has a great economic benefit to our region, without consuming scarce fresh water resources."
"We had confidence that the KMS filtration systems would work well, based on the experience of the Datong Mine, and the system has exceeded our expectations!" said Tian. "By using the ultrafiltration pretreatment, we have minimized the fouling of the reverse osmosis elements, which helps us to reduce our maintenance costs and extend membrane life. The pretreatment system allows us to maintain a high operating flux, and thereby reduce our energy costs."
The Tangshan Steel Works serves as a model of sustainable economic development. Reverse osmosis systems, with ultrafiltration pretreatment, can take polluted and formerly unusable water sources, such as the water in abandoned mines like Datong and Tangshan, and turn it into high quality water that can fuel industrial growth and help quench the drinking water needs of an entire population.
Koch Membrane Systems Inc. (www.kochmembrane.com) has been a global leader in separation and filtration products for over 30 years. A designer and manufacturer of membrane cartridges and elements, as well as complete membrane systems, KMS products are specified for the most demanding applications. To enhance membrane performance, it offers a line of antiscalants and cleaning chemicals, and provides a wide range of maintenance and technical service programs. The company has supplied membranes for over 15,000 systems installed around the world, serving the food processing, life sciences, and general manufacturing industries, as well as providing potable water and wastewater treatment technologies for communities of all sizes. With headquarters in Wilmington, Mass., it's a member of Koch Chemical Technology Group LLC.