signaling the presence of air in working premises of toxic gases and vapors
All the shops, which may release toxic hazards, regardless of the ventilation system must be equipped with special automatic devices for signaling the presence in the air of the premises of toxic gases and vapors.
In industries that use open hardware or equipment that has inspection openings and workers, ventilation, usually arranged with a local suction. To open or periodically opening devices are all sorts of tanks and vats, reactors, thickeners, repulpatory, filters, centrifuges, crystallizers, ovens, mixers, etc.
Vats, reactors, repulpatory, thickeners are supplied with lids that have sight, and boot opening. Venting such devices is achieved by sucking air from their inner cavity so as to entering through the hatches and let the air leaks knockout hazard from the machine. Dimensions of working windows are usually known for designing, other holes and leaks can also be taken into account. Calculation of exhaust air produced in the usual way on the velocity in the openings and leaks from the known formula. The estimated velocity v (in m / sec) is taken depending on the condition of the pollutant and its toxicity.
Multiplicity of exchanges in general ventilation for certain areas of chemical plants (r / h):
liquid chlorine and chlorine products. . 6.10 cryolite and aluminum fluoride .... 3-5
calcium chloride ........... 4-5
Ba ............ 3-5
(Check for heat)
DDT .................. 8-10
chloride and phosphorus oxychloride fosfora10-12
furfural and fluoride ...... 8-10
plasticizers ............ 8-10
hydrochloric acid and zinc chloride. . in-8
hydrochloric acid (storage )....... 3-4
sulfuric acid (storage )........ 1-2
vat dyes ........... 4-5
strong nitric acid ........ 7-9
synthetic rubber (organic
synthesis )................ 10-12
Multiplicity of exchange are given in conventional room height 6.8 m.Sleduet note that sometimes the device is made vigorous stirring the solution with compressed air, the so-called bubbling. This increases the evaporation of the solution and may form hollow droplets. When bubbling air velocity in the openings to take more than when a calm surface of the liquid.
Sometimes the gas release from the device occurs periodically and very rapidly. Thus there is a foaming liquid and a large amount of hollow droplets. In such processes the air velocity in the working aperture should be increased by 50-70% against the calculated values for a peaceful separation of gases. In these cases, is not recommended rate of less than 1,5 m / sec. At a very rough allocation of gas and vapor to prevent the ejection of foam through the working aperture, speed in his section should be taken not less than 3 m / sec. Of course, the amount of removed gas-air mixture should be several times larger than the volume of gases evolved during the same period of time.
When filtering the hot solution, if their temperature is above 50 В° C, there is intense evaporation of the filtered liquid. Vacuum filters, filter presses and other filtering devices are beginning to soar significantly. If only the water evaporates, the local pumps can not hold, but if together with the water evaporates any harmful substance, the local pumps are necessary. For example, when filtering the hot solution of nickel hitting even small amounts of nickel salts in the air causes cutaneous disease.
At a temperature of the filtered solution above 80 В° C soaring becomes so intense that easily formed a fog, which is unacceptable due to reduced visibility. In such cases, cover the filter with the local suction.