the earthquake in Japan caused serious nuclear pollution, followed by
the global nuclear power security construction of the big discussion,
the same in China after several years of inspection and discussion again
to build nuclear power on the agenda. At
present, due to excessive consumption of fossil fuels, humans are
facing the energy shortage and environmental pollution embarrassing
situation. In the global response to climate change, the urgent situation of CO2
emission reduction, the world has a trend of energy change and
low-carbon development, strengthen energy conservation and low carbon
energy structure has become a common choice for energy strategy.
Nuclear power as a clean and efficient energy, not only can increase the energy supply, optimize the energy structure, but also in response to climate change, to achieve low-carbon development has a unique advantage. To this end, countries competing to expand the field of nuclear energy development and utilization of new energy. China as a large energy consumption, the development of new nuclear energy has entered the national strategic layout.
However, after the Fukushima nuclear power plant accident in Japan, nuclear power plant safety issues have been the world's attention, and thus led to a series of discussions, but also the nuclear power plant emergency command center design requirements to a certain height. The emergency command center of the nuclear power plant belongs to the emergency response system of the nuclear power station. The ventilation and air conditioning system mainly undertakes the following functions: When the nuclear power plant accident occurs, ensure that the room temperature and humidity meet the normal operation requirements of the equipment and ensure that the radioactive dose Within the allowable range.
The ventilation and air conditioning system of the emergency command center generally includes two combined air handling units and an air purifier. When the nuclear power plant accident is expanding, the factory environment air there are a large number of radioactive material, air purification unit at this time, the outdoor fresh air and part of the return air purification, removal of airborne radioactive aerosols and radioactive iodine to ensure that the emergency command center Within the staff can be retained.
Nuclear power plant emergency command center air purification unit structure design process is as follows.
1、Design conditions for air purification units
Power Station Emergency Command Center The main function of the air
purification unit is "to heat the fresh air, filter and iodide
adsorption to purify airborne radioactive aerosols (radioactive dust)
and radioactive iodine and provide airflow through electric heaters,
filters and Iodine adsorber channel. "The main performance
parameters and grade of the unit are: rated air volume: 4800m3 / h;
heating capacity: 30KW; safety class: NC; quality grade: Q3; design
specification level: NA; cleanliness level: C
2、Structure Design of Air Purifier
《ANSI / ASME N509-2002 Nuclear Power Plant Air-Cleaning Units And
Components》provides the following general requirements for the
functional design of air purification units:
① If the inlet particle concentration and size can lead to premature failure of the high efficiency air particle filter, a prefilter should be provided in the unit, and in other air purifying units, it is recommended only when it is desired to extend the life of the high efficiency air particle filter Pre-filter.
② When the inlet particle material requires the lowest filtration efficiency of 99.97% (particle size equal to 0.3 microns), in all air purification devices are required to set the efficient air particle filter.
③ When the designed air purification device requires removal of iodine and iodine compounds, it is required to set the iodine adsorber.
④ When carrying the concentration of water droplets in the 1700m3 / h air flow is greater than 0.45Kg, you need to set the defogger.
⑤ In the meteorological parameters of 1% (local) relative humidity of more than 7%, then the adsorber in the air purification unit should use electric heater. For nuclear air purification facilities that are not affected by outdoor meteorological conditions, electric heaters should also be installed when an accident results in a relative humidity of more than 70% of the airflow.
⑥ If an adsorber is used in an ESF air purifier, a rear filter should be provided to filter the carbon particles. For non-ESF air purifiers, if the exhaust gas enters into a person's space, in this case, air is not allowed to carry toner, so it is also advisable to set up a rear filter.
Based on the above general requirements, the nuclear power plant emergency control center air purification unit should include the following functional sections: electric heating section, pre-filter section, pre-efficient filter section, iodine adsorption section, post-efficient filter section.
3、Design of Unit Main Function Section
3.1 electric heating section
The electric heating section is divided into shell and electric heater components. The electric heater shell provides a closed environment for the installation of the electric heater components, and is connected with the unit shell through the flange and the ventilation system and the iodine adsorption unit body. The main function of the electric heater element is to heat the flow of air, reducing the relative humidity of the air to ensure that the iodine adsorber in the required humidity range of work.
3.2 pre-filter section
Due to the system rated air flow of 4800m3 / h, according to the filter national standard module (3400 m3 / h), pre-filter section set up two pre-filter, to remove the air particle size of 5μm or more large particles of dust , While effectively protecting the front efficient filter section. The main performance parameters of the prefilter are: size: 610 × 610 × 50 mm; rated air volume: 3400m / h; efficiency: ≥85% (weight method); initial resistance: ≤ 50Pa; model: nuclear net ZC03; 2 sets.
3. 3 front and rear efficient filter section
The function of the high-efficiency filter section of the pre-purification equipment is to remove the large dust particles with the particle size above 0.3μm in the air and the important function of the whole unit. By setting up two high efficiency filters in this function section, Can make the flow of air up to 99.99% of the radioactive dust is the effect of purification.
The function of the post-efficient filter section is to remove the activated carbon toner or particles carried by the air from the iodide adsorber to ensure that the air flowing out of the unit is completely purified and does not form secondary pollution. In theory, the post-efficient filter section can be set to sub-high efficiency filter, but in order to unify the model of high efficiency filter, reduce the workload of future procurement staff, and management personnel management, post-efficient filter section also set two efficient filtration And the model and technical parameters are the same as those of the front high efficiency filter. High efficiency filter main performance parameters:
Specifications: 610 × 610 × 292 mm; rated air volume: 3400m / h; efficiency: ≥ 99.99% (sodium flame method); initial resistance: ≤ 325Pa; Model: nuclear net VM02; Quantity: front, rear 2 sets.
3.4 iodine adsorption
The main function of the iodine adsorption section is to remove radioactive iodine and iodine compounds in the air, and the core acting element is the iodine adsorber. At present, China is currently using three types of iodine adsorber:
① type iodine adsorber, its size and high efficiency filter the same, the processing air flow is generally 1200 m / h, that is, a rated air flow of 3400m / h high efficiency filter with three I-type iodine adsorber match. Because this type of iodine adsorber can only be installed vertically, if the system air volume is large, may lead to iodine adsorption section than the filter section in the vertical size is much higher, so that the whole unit was "convex" type layout.
② type iodine adsorber, its size is smaller than the I type, and can be installed horizontally, but its processing air flow is generally 567 m / h, that is, a rated air flow of 3400m / h efficient filter with six II type iodine Adsorber match. If the system is large, it may cause the entire unit to be too long in horizontal direction and do not use equipment for processing, packaging, transportation and installation.
③ type iodine adsorber, mainly used in AP1000 technology nuclear power plant reactor type, this type of iodine adsorber can be automatically converted to carbon, but not suitable for the design of this unit, so do not make too much discussion.
As the system air flow of 4800m / h, iodine adsorption section set up a total of eight I-type iodine adsorber. Among them, every four I-type iodine adsorber in parallel for the 1, two levels of iodine adsorption section in series to improve the adsorption of radioactive iodine effect. The main performance parameters of the iodine adsorber are: size: 610 × 610 × 292 mm; rated air volume: 1200m / h; efficiency: ≥1000 (methyl iodide); initial resistance: ≤ 360Pa; Model: I type。
4、Design of important components of the unit
4.1 Pre-filter compression mechanism
The prefilter is made of T / GJ122 type compacting device produced by Nuclear Net, which is simple in structure and reliable in operation. The T / GJ122 compression device is welded to the rack and the filter is moved by adjusting the position of the clamping handle. Note that when installing the filter, first open the handle, the filter has a gasket on the side of the sealing frame, the folding direction of the filter in the vertical direction on the compression tray, put it in place, and then press the handle In place.
4.2 high efficiency filter, I type iodine adsorber compression mechanism
High efficiency filter compression device and type I iodine adsorber compression device are used by the nuclear net production company T / GJ121 type compression device, by adjusting the compression handle to load and unload high efficiency filter, rear high efficiency filter and Ⅰ type iodine Adsorber. Install the handle first to the open position, and then the high efficiency filter, rear high efficiency filter and type Ⅰ iodine adsorber with gasket side of the sealing tower facing the other side on the compression tray, flat push Into place. And then pull the handle to the closed state, that is, to complete the installation. 3.2.3 fire sprinkler system
The iodine adsorption filter unit is equipped with a large water sprinkler system, leaving an interface to an external fire protection system. When the unit fire detection system detects the abnormal temperature rise or combustion of the product within the unit, the fire system can be manually activated to extinguish the fire. Spray system main performance technical parameters: Design pressure: 0.3-0.7MPa; Design flow: 505-770L / min; Interface form: G2 "external thread
The unit sets up three differential pressure transmitters, which are used to measure the differential pressure of the pre-filter, the front-end high efficiency filter and the rear high efficiency filter, and output the remote signal to determine when to replace the filter. Remote signal and nuclear power station control room professional equipment can be connected after the filter to achieve remote monitoring, you can also preset the alarm value and to achieve voice alarm.
The unit is equipped with a humidity transmitter upstream of the iodine adsorption section, and a temperature transmitter is arranged downstream to control the start and stop of the electric heater. When the humidity reaches 40% when the electric heater starts, the temperature reaches 80 ℃, the electric heater to stop working.
4.4 exhaust overflow port
When the iodine adsorber is on fire, the fire sprinkler system opens and begins to inject fire water into the unit. However, due to the increasing temperature inside the unit, the pressure gradually increases, which may lead to the smooth injection of fire water. Therefore, it is necessary to set the exhaust port at the top of the unit to ensure that the air is discharged when the fire water is injected. At the same time, when the fire water filled, the water outflow from the top of the exhaust, this time to determine the water has filled the entire unit, can immediately stop filling water. Therefore, the exhaust port shoulders the exhaust and overflow functions.
A number of drains are provided at the bottom of the unit and connected to the sewer. When the fire was annihilated, the unit of fire water through the discharge.
5、Unit design improvement
5.1 Design of electric heater
the design of the previous electric heater, the designer used to put
the electric heating section between the pre-efficient filter section
and the iodine adsorption section, and the air flow from the electric
heater directly into the iodine adsorption section. The
drawback of this design method is that the ventilation cross section of
the air flow through the electric heating section is larger, when the
system rated air volume is large, the pre-efficient filter section and
the iodine adsorption section ventilation cross-sectional area may be
larger, which will pass The airflow rate of the electric heater is reduced and the heating effect is not satisfactory. If
you want to increase the flow rate of the air through the electric
heater, it is necessary to change the ventilation duct in the electric
heating section, which will make the internal structure of the whole
body become very complicated or cause the appearance effect to be
the electric heating section is arranged at the front end of the whole
unit, and the electric heater element is arranged in a smaller shell,
and both ends of the shell are connected with an air duct and an air
purifier. This design allows the air flow through the electric heating section
of the ventilation cross-sectional area is greatly reduced, and make the
air flow rate and heating effect is guaranteed, but also make the whole
unit more smooth appearance.
5.2 Improved design of iodine adsorption section
The conventional iodine adsorber is arranged in a single row vertical arrangement. The system requires a system rated air flow of 4800 m3 / h. The two stage iodine adsorption sections require at least four I-type iodine adsorbers vertically, so that the vertical maximum dimension of the iodine adsorption section To more than 3 meters, which for the installation, transportation, maintenance, replacement of iodine adsorber and other work will bring a lot of inconvenience. To this end, the unit will be iodine adsorption section designed for the double row of double-layer layout of iodine adsorber, effectively reducing the unit's iodine adsorption section of the height.
Another problem with this is that this arrangement, while addressing the height of the problem, but need to be located in the unit inside the iodine adsorber, you need to reserve at least 1.8 to 2 meters of the maintenance channel. And the installation location of the unit just in the middle of the room, not close to the wall, such as reserved 1.8 ~ 2 meters of the maintenance channel will interfere with the installation of other equipment. To this end, the unit has designed a two-sided door-type sealing door (that is, the front and back of the unit are set to seal the door), so that maintenance personnel from both sides of the unit to replace the iodine adsorber, this program only on both sides of the unit are reserved 1 Meters around the maintenance channel can be.
Command Center Air purification unit is an important equipment for the
ventilation system of nuclear power plant. By setting the function
section in the unit, the air purification can be realized in the
accident state, so that the emergency command center can be staffed. China
Southern is the purification industry, "the only standardized" system
solutions provider, the ISO9001 system certification. Mainly
to provide users with purification equipment, clean engineering,
purification works, clean room, clean room, air filters and other areas
of purification services.