Pressure source of pressure vessel
Pressure vessel pressure sources can be divided into two categories, one is the pressure generated or increased outside the vessel; the other is the pressure generated or increased inside the vessel.
The pressure source that generates or increases pressure outside the vessel is generally a gas compressor or a steam boiler.
Compressors increase gas pressure by mechanical means. Volume compressor by reducing the volume of gas, increase the gas density to increase the pressure of the gas, such as piston or screw compressor that belongs to this category, speed compressor by increasing the flow rate of gas, and its kinetic energy into static pressure energy to increase the pressure of the gas, such as centrifugal or axial flow compressor.
Therefore, the working medium for the compressed gas pressure vessel, its maximum working pressure generally does not exceed the compressor outlet pressure. Steam boilers heat water and evaporate it into water vapor. The specific volume of steam is much larger than the specific volume of water, for example, water at atmospheric pressure is transformed into saturated water vapor at the same pressure, the volume increases by about 1700 times.
When the water evaporates in the closed cylinder, the steam pressure will continue to increase until it reaches the boiler discharge pressure.
Therefore, the working medium for water vapor pressure vessel, its maximum working pressure is also limited to the boiler’s steam pressure. If the steam pressure required by the pressure vessel is less than the boiler’s discharge pressure, it can be depressurized by steam pressure reduction. This pressure generated by the pressure source outside the vessel, generally does not suddenly increase.
Pressure vessel pressure generated in the vessel, generally due to changes in the state of aggregation of the medium in the vessel, the medium in the vessel heat temperature rise dramatically, or the medium in the vessel to increase the volume of the chemical reaction.
The aggregation state of the medium changes, generally for the liquid or solid material is heated to evaporate or decompose into gas.
Evaporation or decomposition out of the gas, the volume greatly increased, but because of the limitations of the container volume, it makes the container gas pressure rise. For example, liquid ammonia, at 0 ℃, the saturation vapor pressure of .4244MPa (absolute pressure), the temperature of 40 ℃, the pressure is increased to 1.534MPa (absolute pressure).
Some polymer compounds are originally solid, if heat “depolymerization”, into the gaseous state of the monomer molecules, will also be due to volume expansion and a sharp increase in pressure.
For example, the specific volume of solid paraformaldehyde is about 0.7L/kg, when it is depolymerized into gaseous formaldehyde, the specific volume is 746L/kg, i.e. the volume increases about 1065 times. If this change of aggregation state occurs in a closed container, a very high gas pressure is generated.
It is relatively rare for a gas to generate or increase its pressure due to an increase in temperature. For an ideal gas, the pressure of a certain mass of gas increases only 1/273 of its pressure at 0°C for every 1°C increase in temperature with a constant volume.
Therefore, when the temperature of a gas increases by a small amount, the pressure increase is not significant. However, if the temperature of the gas increases dramatically for special reasons, its pressure will still increase significantly. For example, if a container containing certain hydrocarbons that are prone to polymerization reactions occurs under certain appropriate conditions, a large amount of polymerization heat is generated, the temperature inside the vessel rises dramatically, and the pressure increases dramatically.
If the volume of the chemical reaction in the closed container, once the reaction is out of control, and the reaction products are not discharged in time, the pressure in the container will increase.
Commonly, such as calcium carbide plus water to produce acetylene reaction, calcium carbide is a solid, water is a liquid, the reaction products acetylene is a gas, as the reaction proceeds, the gas volume will increase rapidly. If the reaction is carried out in a closed container, and the exhaust pipe is not open, the pressure in the container will rise rapidly, and even produce overpressure explosion.
General pressure vessel medium pressure generated outside the vessel, that is, the compressor or steam boiler as its source of pressure. In the vessel pressure pressure vessel is used less, but because the pressure of this vessel is generated in the vessel, the danger is greater, and thus the control of its pressure should be more stringent.
Source: China Pressure Vessels Manufacturer – www.secmachinery.com
www.secmachinery.com is one of the leading china filtration equipment & sanitary stainless steel pressure vessels manufacturer, with professional factory. We focus on the sanitary pressure vessels, filtration equipment research and development, manufacturing, sales and service since the company been established. Our products is widely used on bio-pharmaceutical, food and beverage, fine chemical industry.
If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]