(Image courtesy of NJaj/FreeDigitalPhotos.net.)
Coal to liquid fuel (CTL) conversion requires massive amounts of water – as much as 10 tons of fresh water for one ton of coal-derived fuel, according to some estimates.
This gives CTL plants a large water footprint and creates high volumes of wastewater. This is a two-fold environmental concern:
- Contributing to water scarcity in areas already strapped for water.
- Wastewater discharge polluting land and waterways.
However, an in-development coal to liquid fuel conversion project in China aims to minimize its water footprint and comply with statutory regulations by including a Zero Liquid Discharge (ZLD) water treatment facility as part of the CTL plant.
ZLD is a water treatment process in which all the wastewater produced is purified and recycled for use. This will leave no liquid discharge at the end of the treatment cycle.
The ZLD plant, supplied by Aquatech, will recycle 55 million liters of wastewater per day (2,300 cubic meters per hour) generated by the four million tons per year CTL plant.
The recycled water will be treated to achieve a high purity level, then will be reused in the CTL processing facility. This will eliminate all wastewater discharge from the plant.
Aquatech’s ZLD system is fully integrated and automated and has been specially developed for the CTL market. System components include UFRO (Ultrafiltration and Reverse Osmosis), HERO (High Efficiency Reverse Osmosis) and Unseeded Falling Film evaporators.
This is followed by crystallizers at the back end to solidify the remaining waste to achieve complete zero liquid discharge.
It should be noted that this process is not completely waste-free overall.
Though it is true that the liquid wastewater stream is purified, the remaining solid waste still needs to be disposed of. Dan Bjorklund, director of industrial concentration at Aquatech, explained that this solid waste stream is typically sent to landfills or is beneficially re-used as a feed in other processes.
Aquatech will also supply an ion exchange process for post-treatment of the recycled water to achieve the purity levels needed to reuse the water in the process facility.
Leading the project is Shenhua Ningxia Coal Industry Co. Ltd., a division of China’s largest coal producer Shenhua Group. The Shenhua CTL plant is located in an already dry, water-stressed region in northwest China, making their move toward a minimal water footprint an important endeavor.
For more information, visit Aquatech’s website.