Separation expertise for sustainable and efficient zero-liquid discharge (ZLD)

Zero liquid discharge: ensuring that zero means zero

Non-stop salt slurry dewatering in scorching temperatures

Baotou, China, is the largest city in Inner Mongolia and has a total population of well over two million who have been benefiting from a new, greener power station since mid-2018. To reduce this plant‘s environmental footprint by eliminating wastewater discharge, increasing water reuse, and facilitating the recovery of valuable by-products, the plant operators wanted to apply a zero liquid discharge (ZLD) approach their salt slurry dewatering - a crucial stage in the process.

The challenge:

Ensure that zero means zero in a new power plant

The ZLD process cleans the exhaust gas before sending it to a crystallizer. After this, some kind of solid/liquid separation technology, like a centrifuge or a press, is needed to dewater and recover the salt from the brine. No matter how efficient the previous steps were, the overall efficiency is decided here. For each milligram of solids remaining in the water and each percentage of water remaining in the solids, a price has to be paid, either by the plant operator or the environment.

The overall goal for this plant was to generate power with minimum environmental impact and maximum operating efficiency. And the main separation challenge was created by the high process temperatures required by the crystallizing technology.

Our solution:

Special decanter centrifuge and automation package

ANDRITZ‘s expertise in ZLD processes goes back to the first systems introduced in 1990 and therefore the ANDRITZ experts know that the best choice here is a decanter centrifuge made from a high-grade alloy capable of withstanding temperatures of up to 135 °C.

The special A4 design is able to cope with the scorching temperatures while ensuring the solids emerge as dry as possible, with salt moisture not exceeding 10%. In addition, the design includes lubrication and seals to minimize maintenance interaction and ensure the maximum possible availability of our product.

The Metris addIQ package for smart automation optimizes performance to minimize maintenance and downtime. In addition, the Chinese version of the Human-Machine Interface (HMI) makes the system very operator-friendly. Despite the short, nine-month delivery period, ANDRITZ adapted the order to include a scraper system when the customer mentioned the potential problem of salt being difficult to discharge from the bowl outlet.

Results:

Zero liquid discharge, non-stop operations

The temperature-resistant materials, closed design, and automation features have made the equipment practically maintenance-free while increasing production efficiency to up to 20 tonnes of dried salt per day.
Our automation solution has enabled operation with maximum efficiency as well as helping the maintenance team to plan and optimize the work needed.

ANDRITZ experts in Germany, China, and Slovakia all contributed towards delivering the sophisticated equipment that rapidly overcame any teething problems and adds high value to the customer: uninterrupted operations with zero liquid discharge. The decanter has been running continuously for over 2,000 hours and counting.