Challenge

Dalian Chemical Group, a large producer of a variety of chemicals at multiple plant sites across the People's Republic of China, wanted to expand its operations in Dalian, an industrialized coastal city in the northeast with the country's northernmost warm water port.

Due to increasingly scarce potable water in the region, though, government officials have encouraged industry to adopt other supply options such as more efficient water management, water reuse and desalination. Without access to groundwater or surface water, Dalian Chemical needed such an alternative source for the facility's power plant, which provides electricity and steam to the chemical plant.

The Da Gushan Power Plant includes two 50-MW and one 15-MW coal-fired generators. It requires process water for general use throughout the power plant and more purified water for makeup to the boiler. Feed water comes from the Bo Hai Gulf, a shallow northwestern arm of the Yellow Sea.

Solution

As such, Dalian Chemical looked to desalination via seawater reverse osmosis (SWRO) technology. The China Northeast Power Design Institute provided upstream and downstream intake design as well as ancillary system design, including sanitary systems.

Supervising installation, commissioning and start-up, Siemens provided a double-pass SWRO system that included the Memcor® CP ultrafiltration (UF) system for pretreatment. This included four sets of microfilter skids equipped with Memcor® L20V membranes with a feed flow rate per set of 467 cubic meters per hour (m³/h).
 
The full treatment system consists of:

• Coagulation
• Sedimentation
• Auto-clean screen (or disc) filter
• UF pretreatment detailed above
• A high-pressure SWRO first-pass system made up of four sets with 406 SWRO membranes each at a permeate flow rate per set of 208 m³/h
• A low-pressure process water second-pass made up of four sets with 133 brackish water RO membranes each at a permeate flow rate per set of 171 m³/h
• Final polishing via a mixed bed ion exchange system

Siemens’ scope of supply starts from the disc filter feed pump and ends at the second-pass RO product water. In addition, the system features PX energy recovery devices, which recover 92% of energy and reduce water needs for additional power.

Results

Part of the permeate from the first-pass RO unit is used as utility water around the power station. Another part of this permeate goes to the second-pass RO and the mixed bed ion exchange and, then, is used as boiler feed water.

The SWRO system for the electric power plant at Dalian Chemical Group was commissioned in July 2008. But, due to delays in the chemical plant start-up and regional environmental issues, it isn't yet fully operational. Partial start-up is expected in late 2010.