HOT TOPIC HOUR

ZLD Options include Crystallization, Spray Drying, and Fixation

The webinar yesterday provided a valuable exchange of information among ZLD system and component suppliers.

One of the goals was to compare evaporation/crystallization to the spray drier for coal-fired power plants. All agreed that the comparison needs to be site specific. In some cases the spray drier is less expensive than the evaporation approach but the comparison was limited to FGD wastewater and not the entire plant wastewater discharge. 

The evaporator /crystallizer approaches for Veolia, GE, Aquatech, Oasys and several others were displayed. The spray dryer approach of Mitsubishi/Advatech was discussed and it was learned that B&W and GE are now both offering a spray drier system.  The GE system is an Alstom design which is slated for startup soon at Iatan (Missouri).

The ZLD market is far larger than the $250 million/yr. which is appearing in many articles.

China has thousands of coal-fired power plants and coal-to-chemicals plants, which will employ  ZLD at a cost of more than $10 billion.

Chinese power plants have some ZLD systems using evaporators but are leaning toward the cheaper route of using flue gas to evaporate liquid in the sludge.

The spray drier approach is being pushed by Mitsubishi, URS, and other international companies.

Coal-fired power plants can opt for calcium sulfite scrubbing and chemical fixation of sludge rather than gypsum production and wastewater treatment.

The latest intelligence is that local Chinese companies are developing their own spray drier technologies and it is likely that this will be the option adopted by most plants.

The market for ZLD for shale oil has not slowed as much as anticipated due the rule of unintended consequences. Previously the salty solution was reinjected into new holes. With fewer new holes the ZLD option has blossomed.

The discussion was structured around a quick view of 100 power points filled with process flow diagrams and cost comparisons. This decision guide is intended to help refineries, CTX, and other plant operators make the best ZLD decisions.  For coal-fired power plants there are three options:  

Lime-based scrubbing systems without forced oxidation create soupy sludge. When these sludges are mixed with lime they encapsulate heavy metals and become non leachable landfill.  The same approach can be used with gypsum wash residue after filtration. Sargent & Lundy analyzed a theoretical 500 MW plant and concluded that fixation was the lowest net present value.

The energy consumption in the evaporation of wastewater is an important component. Howden discussed options including a turbo blower which is widely used for its performance capabilities and energy economy.

Veolia has a process which uses high vacuum and allows evaporation at lower temperatures.  This process eliminates the need for softening. Millions of dollars needed for chemicals and disposal are eliminated even though the energy consumption of the system is somewhat higher.

A number of gas turbine combined cycle power plant are using ZLD. The McIlvaine GTCC Supplier Program displays both existing systems and new projects.