DSI and CFB have a Future - Hot Topic Hour September 22

Report by Bob McIlvaine

I learned an amazing amount about dry FGD yesterday. It was 46 years ago when my small scrubber company received a call from Combustion Engineering. One way or another I have been involved with FGD ever since. But I still have a lot to learn. In early 1965 no one knew anything about power plant FGD. By late 1965 there were dozens of people with some knowledge. By 1968 there were hundreds of people with knowledge. Today there are tens of thousands of people with knowledge. As the industry has grown the amount of available information has grown geometrically. Every year I know more about FGD but every year there is more available information which I do not know.

Our Hot Topic Hours are alternating between product orient presentations and collaborative discussions. Yesterday the discussion on dry scrubbing and DSI provided some very valuable insights. The reason was that the panelists collaborated to provide insights not possible in individual presentations. The experts were

David W. South, Manager, Business Development, Amerex Industries, Inc.

John Toher, IJM Consultants

Michael James Widico, Vice-President, Business Development/APC, Lodge Cottrell

Lew Benson, SO₂ Group Leader, Nalco/Mobotec

Keith C. Day, Director, Business Development, Duct Injection, United Conveyor DSI, LLC

There were some broad conclusions reached:

• CFB will play a bigger role than SDA
• DSI will be utilized in a variety of ways
• SO₃ is a major consideration

There were some new potential schemes which may have a place. For example, if you add lime after the particulate collector but before the scrubber, you take out the SO₃ but also provide reagent for the scrubber. You can also use sodium. It will be washed out of the gypsum on the gravity filter. Many utilities are looking at DSI as a bridge technology. Some are doing so just for a few years until the wet scrubbers are installed. Others are looking at DSI as a way to extend plant life prior to retirement. Others are uncertain as to the course of future regulatory initiatives and believe the safest course is the one with the least capital investment.

It is very difficult to generalize on the solution for any particular plant. The reason is that many site specific factors are involved. The parameters affecting the choice between wet and dry scrubbers are

§  Sulfur concentration in the flue gas

§  Capital cost

§  Operating cost

§  Salability of the ash

§  Salability of gypsum or other byproduct

§  Availability of water

§  Comfort level with fabric filters as opposed to electrostatic precipitators

§  Available footprint

§  SO₂  removal efficiency

§  Variation in the future fuel selection

§  Ash disposal costs

§  Wastewater regulations

§  SO₃ removal requirements

§  Mercury removal requirements

§  HCl removal requirement

§  Particulate removal requirements

Particulate may be the ultimate driver. This includes both stack total particulate emissions and secondary particulate formed by the reaction of SO₂ and other elements in the atmosphere. When the Los Angeles authorities are pleased to reduce eight tons of SO₂ for a cost of hundred thousands of dollars per ton it demonstrates where the ambient PM_2.5 rules will take us.

Dry scrubbers are effective SO₃ removal devices. The experts told us that the CFB units will obtain as much 99 percent SO₃ reduction whereas DSI will achieve more than 90 percent. Since total particulate includes condensables and since SO₃ is the main contributor to the condensibles, the various dry technologies may be needed even if wet scrubbers remove the SO₂.

We highly recommend viewing this hour long recording.  The link is https://mcilvaine.webex.com/mcilvaine/ldr.php?AT=pb&SP=MC&rID=50588742&rKey=f4e51c3dc15a7819