1、 Composition of kitchen smoke exhaust system
The kitchen smoke exhaust system is mainly composed of smoke collecting hood, smoke exhaust pipe, fire valve, lampblack purifier equipment, smoke exhaust fan (including muffler), kitchen integrated air supply device, etc. The type and operation mode of lampblack purifier can be selected according to the actual situation. Before installing the lampblack purifier, the actual operating parameters of each part of the smoke exhaust system shall be calculated first, including operating resistance and exhaust volume. If a new project is to be built, the impact of installing a fume purifier on the exhaust system shall be fully considered. If it is a reconstruction project, the exhaust system needs to be recalculated when installing the lampblack purifier. If necessary, the kitchen hood, smoke exhaust pipe and integral air supply device shall be modified, and the exhaust fan shall be replaced.
2、 Smoke collecting hood
The smoke collection hood is generally processed as a whole, including filtering, oil collection, water collection and other equipment, and is mainly manufactured by professional kitchen companies. The appearance shall be uniform, beautiful and easy to clean. When the kitchen is ventilated, a certain amount of fresh air needs to be added. On the one hand, it can balance the air pressure to avoid excessive negative pressure in the kitchen (generally less than 5pa), on the other hand, it can reduce the kitchen temperature and improve the working environment. There are three main types of cooking fume collection hoods:
(1) The simple gas collecting hood is an oil-free gas supply equipment, which is suitable for various flexible places. It is easy to process and install, and the price is low. However, due to the lack of air supply equipment, the air collection effect is poor, which is easy to make the smoke rotate in front of the kitchen staff and cause oil droplets to disperse.
(2) The air concentrator with oil hood and air supply device can better collect the smoke generated during cooking, and the oil drops will not fall off. As long as the air supply is reasonable, the air quality of the kitchen operator's working face is good. However, the installation requirements are high and the investment is large.
(3) Water and gas collection (smoke) cover
The design principle of the water conveyance and gas collecting hood is to form a water curtain circulation after collision with the lampblack to purify the lampblack. The key to affect the use effect of the water conveyance and gas collecting hood is to form a continuous water curtain, and the circulating water system needs to be cleaned regularly. In fact, due to poor management, most water and gas (smoke) caps will not form a continuous water curtain, but can only form intermittent water droplets or small water columns, which makes them unusable.
3、 Smoke exhaust pipe
The horizontal section of kitchen exhaust pipe should not be too long. Generally, the maximum horizontal distance shall not exceed 15m and the gradient shall be greater than 2%. The horizontal end has a movable joint for easy removal of oil. According to the specification, the exhaust velocity shall not be less than 10m/s to prevent oil from adhering to the flue due to low wind speed. Supports attached to exhaust hoods shall be equipped with air flow control valves.
The unreasonable design and installation of smoke exhaust pipe will often lead to smoke in the kitchen, which directly affects the use of smoke purifier. The main reasons are as follows:
(1) The ventilation area of the main exhaust pipe is insufficient and the air flow is large. According to engineering experience, the wind speed in the main exhaust pipe shall not exceed 15m/s. Otherwise, after a period of operation (such as one year), it is easy to cause the smoke exhaust system to be blocked. In the operation practice of the oil fume purifier, in most cases, the smoke exhaust pipe is blocked due to insufficient ventilation area, and the gas velocity in the pipe is greater than 15m/s.
(2) When the smoke exhaust pipe passes through the building beam, the cross sectional area of ventilation becomes smaller, and the resistance on the cross sectional area increases, thus making the air flow smooth.
(3) When the exhaust pipe passes through the building beam or avoids other equipment pipes, a section of exhaust pipe will be lower than the plane of the entire exhaust pipe. After using for a period of time, the oil-water mixture will accumulate in the lower part of the exhaust pipe, which directly affects the smoothness of the exhaust smoke.
(4) The kitchen smoke from different floors is discharged through the same main pipe. On the floor near the exit, the smoke in the kitchen is better, but in the lower kitchen, the smoke is not smooth.
1. There are three types of exhaust fans in common use: axial flow fan, fan cabinet fan and centrifugal fan.
(1) Axial flow fan was widely used before, but it was rarely used after installing lampblack purifier due to low total pressure. However, it is usually used for the design and installation of low altitude lampblack purifier.
(2) The total pressure of the fan of the air cabinet is medium, the air volume is adjustable, and the noise is low. It is usually used for kitchen smoke exhaust system with medium distance from engine hood to smoke exhaust outlet.
(3) The total pressure and volume of the centrifugal fan can be adjusted, but because of the high noise, it is usually necessary to reduce the noise. When the kitchen is located at the bottom of the building, its exhaust fan should be placed on the roof. On the one hand, it can reduce indoor noise pollution, and at the same time, the exhaust pipe is in a negative pressure state to avoid odor overflow. When the fan is placed on the roof, centrifugal fan is usually selected.
2. Measurement of kitchen smoke exhaust
In order to ensure the purification effect, in the actual design, it is required to calculate the exhaust volume in strict accordance with the suction speed of the exhaust hood. The suction speed of the engine hood is generally not less than 0.5m/s.
5、 Oil fume purifier
1. Measurement of treatment air flow:
Generally, there are three main bases for determining the air volume to be handled by the electrostatic lampblack purifier: first, calculate the air volume according to the projected area of the exhaust hood; The other is the number of furnaces; One is the amount of air pumped from the matched suction cabinet.
1) Model selection according to the total projected area (S) of the oil collecting hood: treated air volume=S (m2) × 2500 ≤ oil smoke purifier volume.
2) According to the choice of furnace:
Each standard furnace（ φ= 350mm), air volume 2000m3/h, total treated air volume=number of boilers × 2000m3/h, and then determine the equipment model according to the total air volume.
3) Selection according to the matching of the original fan: the selected purifier model matches the air volume of the original fan.
4) Select according to the matching fan
(1) Calculation of system pipe network pressure loss: system pipe network pressure loss includes local pressure loss and pressure loss along the way. Local pressure loss: pressure loss of each reducer, elbow, inlet and outlet
Pressure loss along the way: pressure loss in straight section
(2) Total fan pressure=(pipe network pressure loss+equipment pressure loss) × （100+20）%
Select the type and specification of the fan according to the total pressure of the fan
Rated capacity of fan=total treatment capacity of composite flue gas purifier × 1.2%
5) The volatile oil fume produced by vegetables is large, and the design capacity of the purifier should be increased by 40%