Ventilation design and calculation of positive pressure explosion-proof container

Ventilation design and calculation of positive pressure explosion-proof container house
Onshore and offshore oil and oil exploration etc might have an explosive gas exploration area, the area belongs to the category of area and the area, machinery and equipment used in this dangerous working conditions, according to relevant regulations, both at home and abroad exposed to the common room or if the atmosphere inside the instrument of oil and gas storage and transportation equipment requires the use of special processing methods, such as internal electric controlling part and control methods for such equipment, power system operation, protection system, refrigeration and heating cooling system, mechanical sparks or electric spark of explosion-proof, and most of these devices cannot be totally explosion-proof and through the certification body. In recent years, the positive pressure explosion-proof container has realized the normal operation of such equipment under such working conditions. In this paper, according to dnv2.7-2, GB 3836.17 and ABS GUIDE, etc.

The introduction
Modern drilling exploration in the field of field devices explosion-proof performance requirements strictly, for possible fire and explosion area known as the danger zone, generally divided into 0 class, class 1, 2 class three areas, the logging area, for example, wellhead centered within 30 meters radius for the level of explosion-proof area (zone 1 / l), 30 meters to 100 meters area for the secondary explosion area (zone 2/2 area). All the equipment in the first-level explosion-proof area must be explosion-proof. According to the actual situation of production safety and customer requirements, most of the equipment in the second-level explosion-proof area is explosion-proof. However, many logging equipment in the market cannot meet the corresponding explosion-proof requirements.

Principle of positive pressure explosion-proof container
The principle of positive pressure explosion-proof container is to meet the explosion-proof technical requirements through the container shell, so that all the ordinary non-explosion-proof machinery and electrical equipment installed in the container achieve the purpose of explosion-proof. The positive pressure ventilation system is the key to make the container meet the requirement of explosion protection technology. Total power opens, first of all, the system automatically open explosion-proof blower system, the explosion-proof centrifugal fan extraction of danger 30 meters distance outside fresh air into the closet, the closet is the air purging and set up more than 50 pa positive pressure, purging after 3 weeks of time, in the case of control condition is met, open the total power supply automatically, you can then open the power supply control power supply, open the positive pressure inside the other electrical equipment, in the process of opening or in the operation of the equipment in the oven, if explosion-proof monitoring control system to the dangerous gas in the oven or short of corresponding positive pressure, and so on and so forth, alarm system alarm warning, if within the prescribed period of time, The control condition in the box cannot be satisfied, or the upper limit of alarm can be reached directly. The non-explosion control system in the box is automatically closed, so as to achieve the purpose of explosion protection.
The following contents will focus on the design idea and method of establishing the positive pressure through ventilation in the positive pressure explosion-proof container. This part is also the key and difficult points in the design.

Design and calculation of positive pressure ventilation
14 feet container project as an example, the positive pressure explosion-proof measures length X width X height = 4267 mmx2438mmx2591mm, top, side and end plate thickness of 4 mm corrugated board, the design temperature to 40 ℃ to 50 ℃, for 2 or 1 area work environment, indoor staff 2, air changes per hour at least 5 times, internal positive pressure value of 50 or more pa, in order to achieve the corresponding positive pressure values, when calculating the corresponding ventilation, need to take into account the overall net space and outdoor space within the connecting duct and the door in order to prevent the indoor and outdoor air convection set directly when opening the door lock the space, Calculate the air volume is about 380 CMH comprehensive factors, choose 1 set of 380 v / 300 pa / 580 m3 / h of explosion-proof pressure centrifugal fan air supply at a distance, centrifugal fan when need galvanized steel shell, explosion-proof motor, blade through explosion-proof processing, won't produce sparks, by 30 to 50 meters flame retardant air hose in safety distance to box for the wind, the fan should be the whole machine has explosion-proof organization explosion-proof certification, by the overall CPFG system (positive pressure explosion-proof control system to firearms) power supply and control.
Two sets of A60 fire valves with explosion-proof actuators are installed respectively in the air inlet and outlet of the box, and a fuse of 70℃±3℃ is built in. When the outdoor air intake exceeds 70℃, the fuse breaks and the fire valve automatically closes. All fire valves are marked with "on" and "off". Fire valves can be either powered and controlled by CPFG system, or opened and closed manually. Fire valves should be certified by explosion proof mechanism. In front of the fire valve, an additional set of manual air volume regulating valve with an Angle of 0 to 90 degrees is set. Manually adjusting the air volume through the adjustment handle has reached the requirement of controlling the pressure in the room.

Design of heating and cooling system in the explosion proof container
If the explosion-proof container is used as a workshop, in order to ensure the appropriate working environment for the personnel inside the box, take the 14-foot positive pressure explosion-proof container project as an example:
Refrigeration: the box can be equipped with a set of bkf-35/220v-1p explosion-proof single-cooling separate wall air conditioner, refrigerant: R410a, noise inside the box: 36.8/40.8db, outdoor noise: 50db. The selected air conditioner is suitable for area 2 or 1 of explosive gas environment. In summer, it is widely used in oil exploitation, oil refining, dangerous environment and offshore oil platform, etc., to keep the indoor environment temperature at about 18-24 ℃ and 80% of the ambient temperature at -7℃ ~ 43 ℃. The inner machine wall is hung on the wall board, and the outer machine is placed in the outdoor depression. The inner machine can choose no explosion proof, and the outer machine needs explosion proof and the whole machine has explosion proof certification. If the air conditioner also needs to cool the machine, it needs to choose different types and categories of air conditioners according to the heat dissipation of the machine.
Heating: add a set of air tube heater at the air inlet and install it at the back end of the indoor fire valve, 220V/4kw, for preheating fresh air at low temperature. This set of air tube heater is non-explosion-proof product, which needs to be linked with the fan. When the fan starts for 3 minutes, the heater starts again.
Note: the cooling and heating systems do not normally run together. They are powered by a safety source and monitored by the CPFG system, and in case of an emergency the power to the system will be cut off.

Choice of air supply fan for the explosion proof container
The pressurized fan of the positive-pressure explosion-proof container is a centrifugal explosion-proof fan. Since the fan always works when the pressurized system is started, the protective gas can continuously replace the original indoor gas, thus ensuring the safety of the positive-pressure container. When calculating the air volume is preliminary consider case no other solder joint clearance leakage air volume, staff into the door and window choose escaping air tightness, if the air leak container welding cracks or personnel in and out of doors, escape the tightness of the window is not enough, equipment layout in the complex, easy to form airflow corner, according to the theoretical calculation of air volume value amounted to less than the corresponding positive pressure value and the change in the volume, positive pressure explosion-proof container to monitor ventilation, installed in the vent flow sensor, we can also ventilation results are verified through the testing data.

Conclusion
As a newly emerged container product in recent years, the positive pressure explosion-proof container still needs to accumulate its technical strength, but it has a great prospect in the future container market and has high added value because of its advanced service boxes. As a system engineering, the design of the pressure-positive explosion-proof room has many other aspects to deal with besides the pressure-positive ventilation and explosion-proof. The pressure-positive explosion-proof container in this paper is summarized as follows:
1. The positive pressure explosion-proof container through achieving explosion-proof enclosure, so that the machine or equipment is no longer needed in the cabinet, is advantageous to the danger zone such as logging instrument selection, is no longer limited to the logging equipment must select explosion-proof type, to the danger zone of instruments and meters broad space in the design and application, saving a high precision instrument input costs, and the positive pressure explosion-proof container as compared to the safety of the casing external space, also greatly improved the security in the area of staff.
2. The ventilation part of positive pressure explosion-proof container mainly includes fan supply and air exchange, and refrigeration and heating system of indoor air conditioner and heater. In the box, the centrifugal exhaust fan is used to supply air for a long distance and finally achieve the purpose of indoor positive pressure. Because the air, the wind as unstable factors, cannot capture, calculation, need to consider when establishing positive pressure and application is required by explosion and ignition control system monitoring equipment real-time monitoring, if abnormal, alarm in time, if cannot be ruled out in the rules set up time is unusual, is the system through the broken brake pressure explosion-proof and firearms control system.

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