Re: Effect of steam space on steam quality

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Comments:
: : : How far above the tubes is your water level? : : : What is the diameter of the boiler shell? : : : Are you having problems with wet steam? : : : Is the water level in the water gauge sight glass normal? : : First of all, thanks for the replies. : : I am doing some theoretical work here on the steam space that would be : : available and the droplet size distribution in the entrainment under : : steaming conditions in a packaged firetube boiler. : : I have a shell diameter of 83 inches, 218 inches long. : : The water level is 2-3 inches over the tubes and under steaming conditions : : after taking into account the level swell, the steam space clearance can go : : down to less than 4 inches, especially at low operating pressures. : I saw your question and, depending on the applicable code, there is : already something wrong. ASME Code requires 4 inches : of water above the tubes for any boiler running at : more than 15 psig steam pressure. The swell you talk : about is not really going to happen, except for : start up conditions. The automatic water level controller : will not feed water until the level has dropped : down to the minimum level, so after initial swelling : the water will start dropping as steam is formed and : the water level will settle down. 10 inches above : the waterline is NOT acceptable in a 650 HP unit, I would : recommend at least 18 inches. The other devastating : effect from a too low steam space is the high horizontal : velocity of the steam toward the steam nozzle. : this will create a wave effect with a higher water : level right under the steam nozzle thus creating more carryover. : The water surface at normal water level should be such : that the steam velocity leaving the waterlevel does not exceed : 10 to 15 m/minute Higher velocities will rapidly (not proportionally) : increase the carry over. : Let me know if this was helpful : Eric