Primer on water treatment technology and power generation

Daniel Alessandri, Pall Power Generation

What factors impact the water treatment market in power generation?

The overall market is in transition. It is still absorbing the effect of capital crunch brought on by the combination of economic slowdown and the Enron effect. Most experts agree that the power market will rebound in 18 months. This slowdown in capital investment is slowing down the rate at which plants upgrade their water supply and treatment systems, just as they do with other capital expenditures. In short, the supply, treatment, re-use of water in power plants is directly linked to the overall health of the market. Water treatment and power production are so intertwined that you could say that electricity is just a by-product of the water cycle. About 80 percent of the steam plant is actually dedicated to the supply, circulation, treatment, or boiling of water. The health of the combustion turbine market is having a similar effect on the water treatment market, albeit from a different set of conditions.

The rate of installations of new combustion turbines has slowed down dramatically, with two major impacts. One, the obvious, is that the market for water treatment on combustion turbines is also slowing dramatically, with the retrofit market being still a few years away. The second very significant development is the consolidation of the water treatment market. The major combustion turbine OEMs are expanding their offering to fuel and water handling systems, partly as a way to offset turbine sales decline, and to provide more reliable sources of revenues through service contracts and overall engineering. The absorption of companies like Betz, Osmonics and Glegg into GE is the perfect illustration of this trend.

Why is water treatment so important to the combustion turbine market?

New combustion turbine technologies actually have more stringent water quality requirements than typical steam plants. For example, condensate systems operate at about 15 to 20 ppb (parts per billion) of silica in the water, where specifications for turbine combustion call for 10 or even 5 ppb of silica in the water. Even though the flowrates are greatly reduced compared to the steam cycle, the quality of the water entering a gas turbine is a key factor in the reliability and efficiency of the combustion, NOx control, fogging, or wet compression. Strategically and economically, good quality water treatment is key to fulfill the promise of local power production, distributed generation, or co-generation in remote areas where water quality is uncertain.

How can technology help make better use of water to produce power?

There are a few key factors in how technology can help resolve some of the water/power constraints. First, technology has to enable flexibility in power generation. The water treatment technology of the future will have to be applied to a wide variety of water sources, needs, and environmental regulations, with consistent and reliable water quality output. This sounds obvious but current water treatment methods cannot achieve this degree of flexibility. Most of what we do to water before we can use it in power production is chemical. Water chemistry is well understood but very difficult to control. The fundamental flaw of a chemically based treatment of water is that awful thing called ‘stoichiometry’. Not only do you have to use very specific compounds for different water types, but you have to use the right amount, and adjust that amount when water quality varies (with seasons, precipitations, wastewater plant efficiency, etc.). This places a great burden on operators, and the whole process is sometimes not so kindly referred to as “black magic”.

Where do we look for the technological silver bullet?

Well, there is probably none to look for. Industrial processes, especially power generation and water treatment deal with the most ubiquitous and diverse natural resource the world possesses; water. So there is for sure no single technology capable of handling all water supply and treatment challenges. The closest the industry is coming to that is the new membrane separation technologies developed in the last 10 to 15 years, with varying degrees of success. Some past experiences with membranes have been less than perfect, to say the least, but the fundamentals of the technology are astoundingly promising. The ability to stop contaminants hundreds or thousands of times smaller than a human hair opens the door to easier, more flexible, and potentially cheaper water management in power plants. The concept of “absolute” separation means that you can ensure that practically 100 percent of contaminants of a given size are eliminated from the water. The smallest dot the human eye can see is about 40 microns in diameter. Microfiltration (MF) membranes work in the 0.1 micron range, while ultrafiltration (UF) membranes work in the 0.01 to 0.001 micron range. When you get that small, you can filter out bacteria (in the MF range) and viruses (some are in the UF range) on top of all the other particulates present in the water.

Could membrane technology eliminate the need for chemicals to treat the water?

Probably not, but it will certainly reduce the need for it. Everything here is a question of balance. Think of it this way: Over 80 percent of chemical treatment of water entering a power plant is there to force tiny particles to agglomerate, coagulate, precipitate, so that they can be filtered out by settling, conventional cartridge filters, multi or mixed bed filter vessels. What if you could catch these tiny particles individually? You would now do most of the work in one single “absolute” step. The resulting water is then so clean (it’s actually of potable quality) that the reverse osmosis (RO) or demineralizing steps afterwards are much more efficient at getting the water ready for use in feedwater or combustion turbines. Chemicals would then play a “fine tuning” role, either targeting individual dissolved compounds if they present a specific threat to the process (dissolved manganese, iron, can be easily oxidized and precipitated), or for safety redundancy (disinfection for example).

What lies ahead?

Well, remember the idea of flexibility of water supply? This is where the next step is, and we are getting very close to it. The power industry knows about the efficiency of membrane filtration, but is still expecting better reliability and durability to make it a cost effective solution. New materials and membrane designs are now allowing very good self-cleaning of the surfaces, the flux rates are improving (the amount of water you can push through a given size membrane) and the overall usability is improving greatly. It looks like the elusive promise of good quality process water, whatever the source, climate or season, is emerging in the short term. New technologies are being proven and challenged everyday, and learning takes place. More importantly, the technology challenges of high efficiency combustion turbines and environmental conservation are driving what could be one of the most important enabling technologies in power generation. Making water management cheaper, easier and more reliable is one very important piece of the puzzle for economic development and power generation worldwide.

Alessandri is a senior marketing manager for Pall Power Generation in East Hills, N.Y., www.pall.com. Contact Alessandri at daniel_ alessandri@pall.com for more information.

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