GB1368067A - Control of the concentration of dissolved solids in evaporator systems - Google Patents

Abstract

1368067 Blowdown apparatus for boiler NALFLOC Ltd 3 Dec 1971 [17 Dec 1970] 60072/70 Heading F4A [Also in Division B1] An automatic blow down apparatus is used to control the concentration of dissolved solids in boiler water. The water is blown down for a predetermined duration at predetermined intervals until a means, which peri odically samples the boiler water, detects a concentration of dissolved solids above a predetermined level; the frequency of blowdown and/or the duration of each discharge is then increased until the concentration has fallen below a second predetermined level, when the original blowdown rate is resumed. In the embodiment shown a boiler 1 has water inlet 2, steam outlet 3, manual blowdown line 4 and automatic blow down line 7. An automatic blowdown valve 9 is controlled by a timing means to periodically discharge line 7 via line 10 to drain line 6, and a valve 22 is controlled to allow a sample of blown down water to pass via condenser 21, to a conductivity cell 23 at a frequency probably the same or lower than the blow down frequency. The conductivity measured by cell 23 is proportional to the concentration of dissolved solids and when the concentration is detected above a first level the cell 23 acts through a relay to short out a duration timer which normally imposes a short discharge time on each blowdown. Cam mechanisms, driven by a common motor, are employed to control the frequencies of blowdown and sampling, and the mechanism for blowdown, in the absence of the duration timer, allows a longer discharge duration. When the concentration has fallen below a second level, which may or may not be coincident with the first, the duration timer is cut back in and the original blowdown rate is resumed.