By how much can the temperature decrease if the ESP is constructed of stainless steel and is uninsulated?
Dear Nishitha
The normal ESP operating temperature of around 150°C is typically near the maximum resistivity of the ash. In general, the low temperature ESP operated at about 150 0C has been used for a long time, but the electric resistivity of some kinds of coal ash is higher than suitable for the ESP in this temperature range. If the Insulation damaged or not provided then this the danger for gas condensation in this case the temperature must be higher than this i.e above 150 0C (may be 180 0C)
Hopper pluggage can be caused by the inadequate insulation and hopper heating
Insulation provides protection for facility personnel as well as working to retain as much hopper wall temperature as possible. Hopper wall temperature retention discourages condensation on the inside of the hopper. Heaters are added to ensure hot metal surfaces immediately above the fly ash discharge.
Proper insulation. Most ESPs use some type of insulation to keep the flue gas temperature high. This prevents any moisture or acids present in the flue gas from condensing on the hoppers, electrodes, or duct surfaces. Because most ESPs are installed in the field, check that all surfaces and areas of potential heat loss are adequately covered. The goal is to reduce the heat loss of the flue gas to a level that will prevent acid or moisture condensation in the downstream equipment, requiring the use of thermal insulation protected by external siding. Improper insulation without covering the support beams can also cause source of condensation. Without a patch, the penthouse roof plates are to be insulated from inside.
Regards,
Prem Baboo
Prem Baboo addresses the question of what is a tolerable loss of temperature. That is, what happens to the operation of the ESP at other than design temperatures.
I read your question differently: "How many degrees of temperature will an ESP lose if it is made of stainless steel and is not insulated?" If that is indeed your question, I suggest that it needs to be reformulated. Temperature change or loss will be affected by:
A less individually case sensitive formulation of the question would be: "What is the heat loss per unit area of ESP wall when it is made of stainless and uninsulated, and how does it compare to the heat loss per unit area for other designs?" This still depends on items 1, 2, and 5 above, and to a lesser extent on 4 as that impacts the velocities near the walls and therefore the heat transfer coefficients.
The answers from that question would then be combined with the factors represented by 3 and 4 to provide a value for the temperature loss.
My apologies if I have mis-read your question.
It can be substantial, even leading to the inability to discharge the stack gas. Some plants have had to add fans to get the exhaust up the stack. An extremely expensive way is to stick it in the side of a natural draft cooling tower. They've done that in Germany. One of the publications I have here is on that subject (An Investigation of the Effects of Flue Gas Injection on Natural Draft Cooling Tower Performance). A plant just up the road from here (Bull Run Steam Plant) had the highest efficiency of any power plant in the world for a decade. They were forced to add electrostatic precipitators, which cost more than twice as much as the entire plant did originally. Then they had to add a wet scrubber. This was already a fairly clean plant. So much for performance records, unless you count losses.
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