Container Diesel Generator Set: How to design ventilation & Noise reduction system

The container-type diesel generator takes the container as the carrier, besides the generator, it is also equipped with an exhaust system, smoke exhaust pipeline, electrical connection system, oil circuit system, lighting system, fire and fire protection system and other components, making it a set of reliable, efficient and environmentally friendly modular standby power platform. Generator set containers provide all the necessary entrances, doors, airflow controls and noise controls to ensure that the generator can operate safely, reliably and with minimal impact on the environment over the life of the generator. In the case of remote fuel supply, the necessary connections are mounted on the sides of the container for easy access. Compared with traditional indoor generators, container diesel generators can be directly placed outdoors, without the need to design and build a machine room. Advantages include:

• Do not occupy the interior building space;
• Support overall factory prefabrication production, short construction delivery cycle, low site construction risk;
• Convenient to upgrade and relocate.

In order to reduce noise, outdoor container diesel generators often add sound cancellation equipment to the standard model, which increases the size and construction cost but greatly reduces noise pollution. In order to reduce the overall noise level of the container and do more and better protection for the container, the larger the size of the container noise reduction box, the permeability will be reduced, which affects the ventilation and heat dissipation of the whole unit. Therefore, when designing container-type firewood, it is necessary to calculate the inlet and exhaust resistance of the whole container to avoid exceeding the limit value of the cooling system of the diesel generator set. How do we do it?

1. Air inlet and exhaust form

The ventilation noise reduction system of a container diesel generator set is usually composed of inlet louvers, inlet louvers, exhaust louvers and exhaust noise reduction boxes. According to the arrangement form of air inlet and exhaust, it can be divided into end into end exhaust, side into end exhaust, end into upper exhaust, side into upper exhaust, side end into upper exhaust and other forms.

The end air intake mode is only applicable to the design of containers without independent tank partitions. If containers adopt independent tank partitions, side air intake mode is usually adopted. Because the end inlet air is arranged at the end of the container, its area is usually limited by the section of the container. Because the side inlet air is arranged at the side of the container, the limited end inlet air is smaller, and its inlet air area is usually larger than the end inlet air. As there are air intakes on the sides and ends of containers, the air intakes of this type are larger than those of other types.

In addition, due to the high exhaust temperature of the cooling water tank of the unit, in order to avoid the arrangement of containers and the impact on the surrounding environment and flow field, the hot air discharged from the cooling water tank is sometimes guided upward in the form of upper exhaust air. The size of the end row container can be 13 meters long, and the length of the top row container is usually at least 14.5 meters.

2. Electric louvers for inlet and exhaust air

The electric inlet and exhaust air louvers are usually single-layer rain-proof louvers, the blade material can be aluminum alloy, and the double-layer hollow structure. The opening Angle of the movable louvers should be large enough to ensure that the ventilation rate can reach 90% when the louvers are fully opened, and the effective inlet air area can meet the operation requirements of the unit when the louvers are arranged in serial with the noise reduction box. The blades should be provided with sealing rubber strips, which should be seamless after completely closed to reduce the heat exchange between the inside and outside of the container in winter. It is generally not recommended to use electric louvers as fire valves. Electric louvers close and open as shown in the figure below.

Each louver is equipped with a push rod actuator and the start-stop linkage of the unit. Usually, the operation signal of the unit is taken as the linkage signal of the electric louver actuator. The electric louver opens when the unit runs and closes when it stops. In order to ensure that the louver opening and closing state can be monitored, the actuator must have open and close signal feedback. The actuator shall be able to fully open the louvers within 8s and be equipped with a manual opening and closing device so as to manually open the louvers to avoid unit shutdown in case of electrical failure. The clearance between the louver frame and the movable louver should be small enough to maximize the overall sealing performance. In addition, stainless steel rodent-proof mesh must be made on the air exhaust surface inside the box. Usually, the rodent-proof mesh with a diameter of 10mm×10mm can meet the functional requirements.

3.  Inlet and exhaust air noise reduction

Noise reduction boxes are installed in the inlet and exhaust vents of containers for air inlet and exhaust noise reduction. Noise reduction plates are uniformly fixed on the frame of the noise reduction box. The thickness and clearance arrangement should ensure that the effective ventilation rate of the noise reduction box can reach more than 60%. The inside of the noise reduction sheet is noise reduction rock wool, and the outside is covered with galvanized mesh plate. Common noise reduction tablets have the following forms: L-shaped bending noise reduction tablets; Straight-through noise reduction film; Inverted V noise reducer. L-shaped noise reduction tablets are mostly used for side inlet air noise reduction, straight type noise reduction tablets are mostly used for end inlet air and end exhaust air noise reduction, and inverted V-shaped noise reduction tablets are mostly used for side inlet air noise reduction. In addition, L-shaped bending noise reduction sheet and inverted V-shaped noise reduction sheet have a certain water retaining effect, which can prevent part of rainwater from being carried to the generator area with the inlet wind. The attenuation amount of straight-through chip noise reduction film can be estimated according to the following formula:

∆ L = (phi) (alpha) * P * L/S

Where, ∆L — noise attenuation, φ(α) — noise attenuation coefficient, P — effective air inlet channel perimeter, L — effective air inlet channel length, S — effective air inlet channel cross-sectional area, noise attenuation coefficient can be determined according to the specification of noise reduction rock wool.

Usually, because the area of end air intake is relatively small and the air inlet is far from the generator, it is recommended to use straight-through noise reduction plate. The air inlet area of side air intake is relatively large, but the air inlet is close to the generator. It is recommended to preferentially use noise reduction plate with water retaining function. When the inlet wind speed is high, a rain shield can be installed outside the inlet of the container to prevent rainwater from being carried to the generator area along with the inlet wind.

4. Inlet and exhaust air speed estimation

The wind speed of inlet and exhaust air is related to the performance specifications and installation forms of electric louvers and noise reduction boxes. In engineering applications, the wind speed of inlet and exhaust air can be estimated according to the following principles:

Electric louver area S_ louver, noise reduction box windward area S_ louver, S_min=Min(S_ louver, noise reduction), electric louver ventilation rate ρ louver, noise reduction box ventilation rate ρ noise reduction, air volume V. Usually ρ_ louver >ρ_ noise reduction, the inlet and exhaust wind speed v is between V/(S_min×ρ_ louver ×ρ_ noise reduction) and V/(S_min×ρ_ louver), the comprehensive ventilation rate of electric louver and noise reduction box is usually about 70%.

5. Calculation of air inlet and exhaust resistance

The inlet and exhaust air resistance is the key parameter to be considered in the design of the container firewood box. In order to have lower noise and better rain resistance, the length of the noise reduction box should be extended and the permeability should be reduced, which will increase the ventilation resistance, resulting in the reduction of ventilation volume and heat dissipation capacity. Therefore, in the design stage, it is necessary to check the ventilation resistance of the intake and exhaust air, which is lower than the allowable value of the ventilation system of the diesel generator set. Usually, the ventilation resistance of the container is about 200Pa. It is also required that the water tank of the diesel generator set can ensure its heat dissipation capacity under the condition of high ventilation resistance.