Energy Consumption in Chlor-Alkali Industry Today

By Li Sugai, China Chlor-Alkali Industry Association

Geographic distribution has gradually rationalized & development stabilized

China makes more than 70 major chlorine-consuming products today – mainly PVC, synthetic hydrochloric acid, other hydrogenated products, as well as hydrogen fuel for boilers and power stations. For PVC production, the calcium carbide process co-exists with the ethylene process, but the calcium carbide process is favored by China’s energy economy. The chlor-alkali industry has developed rapidly in Northwest China due to the region’s wealth of coal resources – particularly in Xinjiang, Inner Mongolia and Shaanxi.
Outdated facilities have been aggressively phased out during the Twelfth Five-Year Plan period (2011-2015). Enterprise clusters and industrial parks are hallmarks of the recent development of the chlor-alkali industry. One example is the integration of the calcium-carbide PVC industrial chain, with Xinjiang Tianye (Group) Co., Ltd., Yibin Tianyuan (Group) Co., Ltd. and Xinjiang Zhongtai Chemical Co., Ltd. setting the pace. A second example is the industrial chain for recycling chlorine resources and coordination of multiple sectors, principally occurring in  Shanghai Chemical Industry Area and Ningbo Wanhua Area. Evident advantages are achieved in coordinating industrial sectors, comprehensive utilization of resources, sharing utility facilities, recycling wastes, efficient control of pollutants and reduced logistics cost. After a period of rapid development and a period of slow but stable development, the pace of transformation and upgrading in the chlor-alkali industry is quick. And geographic distribution has been made rational: regions with different industrial development features have jelled gradually, such as the eastern coastal region, the central region and the western region.
Last year, there were 158 caustic soda producers in China with a combined capacity of 39.45 million t/a (29.21 million t/a using the ion membrane process and 0.24 million t/a using the diaphragm process). There were 75 PVC producers, with a combined capacity of 23.26 million t/a (18.51 million t/a using the calcium carbide process; 4.53 million t/a using the ethylene process; and 0.22 million t/a using the natural gas process).
After the development pace of the chlor-alkali industry gradually stabilized, average annual growth of both caustic soda and PVC capacity has been slowed steadily. The shift from capacity expansion to economic restructuring and industrial transformation/upgrading is complete.

Energy consumption is being reduced by 23% during the Twelfth Five-Year Plan period

Technical progress has become a leading driver to transform and upgrade the chlor-alkali industry. Several chlor-alkali technologies have seen R&D breakthroughs and sound application, in clean production, energy-saving, production safety, pollution control/treatment and other equipment. The level of comprehensive resource utilization keeps going up. Compared with the Eleventh Five-Year Plan period (2006-2010), energy consumption and water consumption per unit of output have been reduced by 23% and 47%, respectively. Emission intensity of major pollutants has been slashed. For mercury pollution, a big issue of the chlor-alkali industry, R&D and applications have both seen breakthroughs. Low-mercury catalyst processes have gained extensive applications, and some leading enterprises have moved on to R&D and commercial application of mercury-free catalysts and mercury-free process technologies.
The chlor-alkali industry is energy intensive. Last year, caustic soda capacity was 39.45 million t/a and output was 32.84 million tons. Power consumed in the electrolysis of caustic soda was around 8.0 billion kWh. Caustic soda production used around 2% of China’s total power consumption in industrial sectors (that total being 392.1 billion kWh) in December 2016, according to National Bureau of Statistics. Comprehensive energy consumption per ton of 30% caustic soda was 328 kg standard coal in 2016. Electrolytic tanks take an extremely high proportion of that.

New energy-saving processes are used

In recent years, chlor-alkali enterprises in China have constantly promoted energy conservation in the chlor-alkali industry by “walking on two legs”: actively introducing advanced technologies from abroad and conducting R&D for themselves.

1. Zero polar distance (membrane polar distance) electrolytic tank technology

Most chlor-alkali plants constructed in China after 2008 use membrane polar distance ion membrane electrolysis technology for caustic soda production, making that technology a driver of major achievements in energy conservation and emission reduction. Zero polar distance NBZ-2.7 electrolytic tanks developed by Beijing BlueStar Chemical Co., Ltd. through its own efforts have produced sound results in production since 2009. The technology is not only suitable in new construction but can also serve in renovating electrolytic tanks with polar distance into electrolytic tanks with membrane polar distance.

2. Oxygen cathode caustic soda electrolysis

Oxygen cathode hydrolysis technology is a new electrolysis technology developed in recent years for caustic soda production. A pilot project for “oxygen cathode low tank voltage electrolysis technology for the production of caustic soda using the ion membrane process” developed by BlueStar (Beijing) Chemical Machinery Co., Ltd. in collaboration with Beijing University of Chemical Technology passed examination by the Ministry of Science and Technology in July 2017.
R&D for oxygen cathode technology already has quite a long history outside China. Industrial use of the technology to produce caustic soda was developed by Bayer and has been commercialized. The first commercial oxygen cathode unit in China has already started operation in Binhua Group Co., Ltd. The project uses electrolytic tanks from Ude-Denora and the oxygen cathode technology from Bayer. Construction of an 80 kt/a caustic soda unit is complete, and a capacity of 40 kt/a was put on stream in 2015. Energy consumption in an oxygen cathode unit can be nearly 26.7% lower than for a conventional cathode (nickel net + active coating) unit operating at the same current density, in theory.

3. Hydrogen fuel cell technology

Hydrogen fuel cells convert hydrogen into electric power. On January 9, 2015, Yingchuang Sanzheng (Yingkou) Fine Chemical Co., Ltd. signed a cooperation agreement with Dutch companies, MTSA Technopower, Nedstack Fuel Cell Technology and Akzo Nobel Industrial Chemicals. Yingchuang Sanzheng then introduced technologies from the three companies of Netherlands, used its own hydrogen resources co-produced in chlor-alkali production and constructed the first 2MW hydrogen fueled power station in the world. The power station, as a demonstration project, has gained support of EU hydrogen energy utilization projects. It was completed and put on stream in August 2016. If hydrogen co-produced in the chlor-alkali production is totally used in fuel cell power generation, 30% of power, including 20% of electric energy and 10% of heat energy, consumed in electrolysis units of chlor-alkali enterprises will be recovered.

4. Hydrogen chloride synthesis waste heat utilization

To produce hydrogen chloride gas from hydrogen and chlorine, new hydrogen chloride graphite synthesis furnaces have been developed, with emphasis on energy conservation and environmental protection. They are also used to co-produce 0.8MPa steam. They work by using graphite as a third raw material. They are suitable for use in quite a few chemical sectors – such as chlor-alkali and polysilicon – and have special features of efficient energy conservation, zero waste emission, long service life and high added value.
While synthesizing one ton of hydrogen chlorine gas, 0.65-0.80 tons of low-pressure or medium-pressure steam can be co-produced. 0.2-1.6MPaG low-pressure or medium-pressure steam co-produced in the hydrogen chloride synthesis system can directly enter low-pressure or medium-pressure steam pipelines.

5. Carbide slag slurry acetylene recovery

Carbide slag slurry vacuum-pumping desorption technology can be used to desorb and recycle the acetylene gas contained in carbide slag slurry. Solubility of the acetylene gas in the slurry is closely related to temperature and pressure. In the process, the slag slurry is put in a closed vessel for vacuum pumped pressure reduction, and the dissolved acetylene gas is desorbed and available for recycling.