In addition, the oxygen molecules in the space above the water surface are discharged or converted into other gases, so that the partial pressure of oxygen is zero and the oxygen in the water constantly escapes. Using physical methods to remove oxygen is to separate oxygen from water by physical methods, such as thermal oxygen removal, vacuum oxygen removal and analytical oxygen removal. Thermal oxygen removal generally includes atmospheric thermal oxygen removal and jet oxygen removal. The principle is that the boiler feed water is heated to the boiling point, so that the solubility of oxygen is reduced, and the oxygen in the water continuously escapes, and then the oxygen generated on the water surface is removed together with the steam, so that various gases (including free CO2 and N2) in the water can be removed, such as NH3 in the water treated by the magnesium-sodium ion exchange method. Deaerated water will not increase the salt content, nor will it increase the dissolved amount of other gases. The operation and control are relatively easy and the operation is stable and reliable. It is the most widely used deoxygenation method at present. To ensure that the thermal deaerator has a reliable function.
The design and operation shall meet the following conditions:
A. increase the contact area between water and steam to make water evenly distributed.
B ensure that there is a pressure difference between the dissolved pressure of oxygen in water and its partial pressure on the water surface.
C 104℃ is generally used to ensure that water is heated to boiling temperature under the working pressure of deaerator. Thermal deoxygenation technology is a mature technology with wide application, but there are still some problems in practical application: first, the soft water after thermal deoxygenation has a high water temperature, which is easy to reach the vaporization temperature of boiler feed water pump, making the feed water easy to vaporize during transportation; When the heat load changes frequently and the management can't keep up, the temperature of deoxidized water
Thirdly, the gas consumption of the boiler room is increased and the effective external steam supply is reduced.
Fourthly, thermal oxygen removal has certain limitations for small fast-loading boilers and occasions requiring low-temperature oxygen removal, and cannot be used in pure hot water boiler rooms. For thermal deaerating boilers, when installing new boilers, atmospheric thermal deaerators are installed on the ground. The deaerated high-temperature softened water pipeline passes through the soft water tank, exchanges heat with the water in the soft water tank, then slides to the boiler feed water pump and enters the boiler through the economizer. This improvement can first reduce the vibration and noise of the boiler room, improve the working environment of the boiler room, and also reduce the engineering cost of the boiler room. Secondly, through the heat exchange in the soft water tank, the water temperature in the soft water tank is improved, and the heat is not wasted, which is equivalent to the inlet temperature of the deaerator. The time for deaerator to heat the inlet water to saturation temperature is also shortened, which is beneficial to achieve the expected deoxygenation effect. (1) Low-grade waste heat can be used for vacuum oxygen removal, and softened water can be heated by jet heater;
(2) It can be installed at low level in stages, with reliable deoxygenation, stable operation, simple operation and wide application range.
(3) Since China has vigorously carried out energy-saving work, more and more industrial boiler rooms have used this method to remove oxygen. At present, a new type of analytical deaerator is generally used in analytical deoxygenation, in which a heater is used to replace the original boiler flue gas for heating, and activated carbon and catalyst are used as reducing agents, which greatly reduces the occupied area of the equipment, increases baffles to control the water flow inside the analyzer, and increases small holes and perforated pipes to make oxygen-containing gas in the water fully escape, thus achieving good deoxygenation effect.
The analytical deoxidizing equipment is small in size, easy to manufacture, low in steel consumption, low in investment, convenient to operate and reliable in operation, and does not use chemicals, thus reducing environmental pollution. The deoxidizing can be carried out at low temperature and the deoxidizing effect is good. At present, it has been widely used in hot water boilers and single-layer industrial boilers in China. Its disadvantage is that it can only remove oxygen in water, but not other non-condensable gases, and the content of carbon dioxide in water has increased; The water surface of the water tank can't be sealed, and sometimes the deoxidized water comes into contact with the air, which affects the deoxidizing effect. Analysis of oxygen removal has the following characteristics:
(1) The water to be deoxygenated does not need preheating treatment, so the steam consumption of the boiler room is not increased.
(2) Analysis of deoxygenation equipment occupies less land and consumes less metal, thus reducing capital investment.
(3) The oxygen removal effect is good.
Under normal circumstances, the residual oxygen content can be reduced to 0.05 mg/L after deoxygenation.
(4) The disadvantage of analytical deoxygenation is that the equipment adjustment is complicated, and the piping system and deoxygenation water tank should be sealed. As early as 1960s, this technology was widely used in many boiler rooms at home and abroad, but the reactor at that time was located in the flue and could not adapt to the change of heat load. Therefore, the use of this technology was once restricted. By the 1990s, several second-generation analytical deaerators with electric heating reactors were developed, which made this technology develop rapidly. In particular, the new analytical deaerator developed by Tsinghua University in cooperation with the Design and Research Institute of the Ministry of Mechanical and Electrical Engineering has overcome the original shortcomings and deficiencies. The heating furnace is separated from the reactor, and the gas from the desorption deaerator is heated by the heating furnace, and the heated gas is deoxygenated when passing through the reactor, so that the oxygen-containing gas in the water to be deoxygenated is fully decomposed, and the operation reliability and deoxygenation effect are ensured.
The volume and power consumption are smaller than the original equipment. The new analysis system is adopted, which saves the oxygen tank and solves the sealing problem of the original water tank. The operation of several boiler rooms proves that the analytical deaerator is simple in operation, low in investment, reliable in operation and good in effect. But at the same time, there are many factors that affect oxygen removal, and only oxygen can be removed without removing other gases. When water passes through the resin layer, the dissolved oxygen in the water is reduced from zero valence to negative bivalence, forming oxide (copper oxide). After the resin fails, it can be reduced by ammonia, and Cu2+ is absorbed by the exchange gene on the resin. It should be noted that the discharged water contains trace ammonia and cannot be used as drinking water. The deaeration water tank should be isolated from the air, and two deaeration water tanks should be set at the same time to ensure the continuous supply of deaeration water. It is an urgent problem to pay attention to new technologies, new materials and new achievements, be brave in exploration, improvement and innovation, and seek a method with good oxygen removal effect, reliable operation, simple management and low investment.
In recent years, the progress of zero-position hot bubble membrane oxygen removal, vacuum oxygen removal and analytical oxygen removal is a good example. There are many ways to remove oxygen from boiler feed water. In order to operate efficiently, economically, stably and safely, it is necessary to combine the boiler type and actual situation, comprehensively consider the thermal parameters, water quality, tonnage, load change and economic conditions of the boiler, and make a selection according to local conditions. The dosage in the pot is: softened water is used in the pot, and10kna3po4 or 20kgNa3PO4 is added per ton of water. Check the PH value of boiler water every 5 days, and the control index is 10~ 12. If the alkalinity is low, add some lye. Wet maintenance is suitable for boilers that have been shut down for a short time, and it is not suitable for wet maintenance in areas with low temperature, so as to avoid freezing of boiler water and damage to boilers.