Incineration Plant Waste Grab Crane Selection: Key to Efficient Operations

Incineration plant waste grab crane is mainly responsible for feeding the rubbish incinerator and undertaking the work of rubbish handling, mixing and palletising. The working environment of the whole machine is harsh, the working load is heavy, the maintenance is difficult, and it is easy to break down. Once the rubbish grab crane fails, it will directly lead to the paralysis of the whole waste incineration plant. For large-scale waste incineration plant, this may cause the chaos of the entire urban domestic waste disposal system, because, in the local area to build a large-scale waste incineration plant full-load waste disposal capacity replacement capacity is by no means easy. Therefore, according to the scale of waste incineration plant, process needs to correctly select and configure the rubbish grab crane is very important. Generally speaking, the selection of rubbish grab crane is related to the following factors: 

1. Rubbish type; 
2. Rubbish treatment capacity; 
3. Rubbish storage pit; 
4. Mixing; 
5. Stacking; 
6. Feeding; 
7. Into the rubbish time.

However, with the expansion of the scale of waste incineration plant, the above factors alone can not meet the requirements of the rubbish grab crane selection. For large-scale waste incineration plant, rubbish grab crane selection should also consider the number of grab cranes, feeding cycle, grab volume and other factors.

1 The Number of Incineration Plant Waste Grab Crane 

Previously, the number of rubbish grab cranes was generally set according to the size of the incineration plant (as shown in Table 1). With the expansion of the incinerator’s single furnace scale, the rubbish grab crane settings should not only consider the size of the whole plant, but also consider the number of incinerator stations and the number of cranes on the ease of operation.

The number of rubbish grab cranes should follow the following principles: 

1. To meet the requirements of the incinerator feed volume; 
2. The same track arrangement of no more than 3 units; 
3. The number of actual commissioning does not exceed the number of incinerator feed hopper, it is desirable to standby 1; 
4. 1 grab crane corresponding to the incinerator should not be more than 3 units.

Large waste incineration plant grab crane should be set up 2 or more. Incineration line in 3 or less is recommended to configure 2 cranes, the general situation is that 1 running 1 standby, each output can meet all the incineration line feeding requirements and general mixing work.

The same track has more than 2 sets of grab cranes operating at the same time, the crane activity space is greatly reduced, in order to avoid collision, the operation requirements are higher. Due to the huge scale of the waste incineration plant, when more than 4 sets of grab cranes are in use at the same time, it is recommended to adopt the waste pool separation method or double-deck track arrangement. Singapore Da Shi Nan incineration plant (4320t / d) and Shenzhen East waste incineration project (5100t / d) are used in the rubbish pool pool method. There is no application example of double-deck track arrangement, and there are limitations such as restricted operation view and easy collision of grabs.

2 Feeding Cycle 

The determination of the feeding cycle of the rubbish grab crane is not only related to the capacity of the rubbish incinerator to process rubbish, but also related to the operating cycle of the rubbish grab crane and the ratio of the time that the grab engages in feeding operations.

Rubbish grab crane operation cycle is the rubbish grab crane feeding operation 1 time required, that is, from the grabbing rubbish, the grab rolled up, walking, moving across to the rubbish incinerator inlet, and then the grab open, and finally moving across, walking, down to the original position of the time required. When the above speed and the operating distance of the rubbish grab crane are determined, the operating cycle of the rubbish grab crane is determined. Table 2 shows the commonly used working speed of the rubbish grab crane, according to the length and span of the rubbish pool, the operating cycle of the rubbish grab crane is generally selected as 2~4 min.

The normal operation of a waste grab crane requires sufficient time for mixing, blending and stacking, in addition to grabbing waste to feed the waste incinerator. In addition, in order to reduce the failure rate of the rubbish grab crane and the labour intensity of the operator, it is also necessary to leave a certain amount of rest time. Therefore, the time that the grab is engaged in feeding per unit of time is only a part of it, and this time ratio takes the value of 1/2, i.e. one grab is used for feeding for only about 30 min per hour. Therefore, the feeding cycle per hour is 8 to 15.

3 Garbage Grab Volume 

The volume of the grab should be determined in accordance with the incinerator incinerator serviced by the crane to handle the amount of rubbish per hour and the work cycle, generally calculated in accordance with the hourly feeding 8~15 feeding cycle. In order to reduce the crane’s workload, reduce the failure rate, it is appropriate to feed 8 ~ 10 feeding cycle per hour to calculate the selection.

Through the rubbish incinerator processing capacity can be calculated by the amount of grapple 1 time feeding G (t), and then according to the density of rubbish in the grapple D (t/m3) and feeding the grapple fullness f (volume utilisation), the actual volume of the required grapple is calculated V (m3) = G / (Df). Usually the density of uncompressed rubbish in the rubbish pool is 0.30~0.45t/m3, the density of rubbish in the grab is about 1 times more, that is, the compression ratio is taken as 2:1, and the value is taken as 0.7t/m3, and the fullness of the grab is generally 0.9, so the density of the hopper is generally taken as 0.63t/m3.The technical parameter of rubbish grab is shown in Table 3.

The feeding capacity of the rubbish grab crane depends on the volume of the rubbish grab, the larger the grab, the stronger the feeding capacity. But in terms of ease of operation and flexibility, the rubbish grab should be small rather than large, grapple crane grab the maximum tension angle diameter should be taken as 1/5 ~ 1/4 of the width of the rubbish pool. in the case of a certain amount of feed per unit of time, the advantages and disadvantages of the size of the selected grapple volume comparison of Table 4.

Grab volume can not be determined solely on the basis of feeding capacity, to take into account the size of the waste pool and the convenience of operation.

4 Refuse Grab Crane Configuration Analysis 

Table 5 Comparative analysis of the configuration of refuse grab cranes for different sizes of large-scale waste incineration plants for commonly used grab volume.

Note: There are more application examples of grab volume of 6, 8, 10m3; less application examples of grab volume of 12m3; no application examples of grab volume of 14.5m3.

Rubbish grab crane configuration engineering examples are as follows:

Shanghai Jiangqiao domestic waste incineration plant: 1500 t/d (500 t/dx3 units), rubbish crane 9m3x2 units, 1 with 1 standby, an average of 11 feeding cycles per hour.

Taipei Muzha Waste Incineration Plant: 1500 t/d (375 t/dx4 units), rubbish crane 10 m3x2 units, no standby, average hourly feeding cycle 5.

Kaohsiung South District Waste Incineration Plant, Taiwan: 1800 t/d (450 t/dx4 units), 8 m3x3 rubbish cranes, 2 with 1 standby, average hourly feeding cycle of 8.

Netherlands Amsterdam waste incineration plant: 2880 t/d (720 t/dx4 units), rubbish crane 12 m3x3 units, 2 with 1 spare, average hourly feeding cycle 8.

Singapore Taisinan incineration plant: 4320 t/d (720 t/dx6 units), rubbish crane 10 m3x4 units, no backup, average hourly feeding cycle 7.

5 Other Factors 

5.1 Grab Hydraulic System 

Large waste incineration plants generally use hydraulic grab, which has a quick grab switch action and a large gripping force. But because the hydraulic centre, hydraulic cylinders and flaps and other equipment installed directly on the grab, easy to deface, maintenance should be adequate, hydraulic system maintenance requirements. In the selection should pay attention to the following points: 

1. Motor power should be large rather than small; 
2. Hydraulic unit using variable flow type is preferred to fixed flow type; 
3. Hydraulic pipeline should be set up more than 2 channels of pressure protection, one located in front of the exit of the hydraulic machine, a set of control valves in front of the group; 
4. Internal hydraulic hoses should be shortened as much as possible to reduce vibration wear and tear of broken pipe chances; 
5. Hydraulic resistance should be as small as possible in order to reduce the operating temperature.

5.2 Electrical System 

electro-hydraulic grab due to the fast lifting speed, height and other reasons, the cable is easy to be pulled to cause failure, the current engineering practice successful solutions: one is to remove the cable reel drive motor, cable reel and wire rope reel through the chain connection synchronised to achieve; the second is to configure each cable with a slightly shorter toughness of the synchronous rope. 2 ways to ensure that the cable in the process of lifting and lowering only to bear their own mass to increase the life of the cable. Quality to increase the life of the cable. In the configuration of the electrical equipment, used to consume excess power resistor heat sink, due to the heat generation is amazing, should be placed in a different room with the electrical disc room and installed cooling system to ensure that the operation of the control circuit is stable.

6 Conclusion 

With the expansion of the scale of waste incineration plant especially the expansion of the incinerator single furnace scale, the selection of rubbish grab crane should not only be considered to meet the requirements of the feed, but also comprehensively consider the number of grab cranes, feeding cycle, grab volume, in order to ensure the convenience of operation and reliability of operation.

Reference source: https://www.nstl.gov.cn/paper_detail.html?id=a8d6a31c78960cfce832a1a6b861d32b

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