Article Teaser - wp 8136
White Paper

Successful Commissioning of KREISEL Ceramic Rotary Feeder at PPC Hercules

Written by Visser, J.D., Mayimele, N. & Dikty, M. edited by mhd on 5. Apr. 2016

Grinding aid: To reduce the energy input during the grinding, grinding aids are used. However, these greatly change the conveying and fluidizing behaviour of bulk solids, because they influence the intermolecular forces. The experience of recent years has shown that grinding aids can also strongly influence the compression behaviour of the bulk solids. For the screw pumps this resulted in a capacity reduction of 30%. In this context, the installed 132 kW motor proves itself as under dimensioned. The rotary feeder does not produce the bulk solid compression for sealing. Consequently, the grinding aid has no negative effect on the conveying and driving capacity of the rotary feeder.

Covering of the inlet area: If the inlet to the screw pump is irregularly and the screw pump is operated close to the capacity limit, then the coverings of the inlet area cause the capacity reducing. If the pump surge bin overloads of bulk solids, then the compressed air from the plug cannot be discharged to the inlet. The air is transported through the plug. The plug is unstable and cannot seal against the current conveying line pressure. It causes the capacity reduction. The constructive design of the inlet of the rotary feeder separates the dust removal area from the inlet area. Overfilling of the inlet leads therefore primarily to a capacity increase as to a reduction.

Wear during under load operation: If too less bulk solids mass flow are fed to the screw pump, so the necessary sealing plug cannot be set up sufficiently. The plug breaks and the conveying air flows into the inlet area at high speed. This acts as a sandblasting on the screw. In the ceramic-lined rotary feeders, this effect is not negative. There would be the additional option of wear reducing due to speed reduction.

Energy consumption during lower load operation: For the rotary feeder as inlet component is possibly: If the mass flow drops, so the necessary conveying line pressure drops too. If the conveying line back pressure drops, so the motor current consumption of the pressure generator drops too. Different, however, in the screw pump conveying: Here the influencing component is the nozzle (Fig. 6, item 9) in the outlet housing. As with any nozzle the pressure loss increases with increasing flow rate capability. If the pressure in the screw pumps conveying drops now in the screw pump conveying pressure in the delivery line, so the operating volumes of the conveying air increase. This leads to a velocity increase. The pressure to the nozzle falls significantly; however, the pressure after the nozzle falls only slightly. Thus, the lower load operation is energetic highly disfavoured in screw pumps.

Wear reduction due to speed reduction: The wear on the ceramic rotary feeders depends on the factors bulk solid hardness, the bulk solid shape, the pressure difference over the feeder and the speed of the feeder. During the adjusting the rotary speed to the respective conveying bulk solid mass flow, the wear can be reduced. This is not possible with screw pumps. The high rotary speed of the screw shaft is required to perform the sealing function.

Influence of the back pressure on the pump motor: The motor size of the screw pump depends almost linearly on the back pressure in the conveying line. This already results the motor sizes of 30 kW to 250 kW in average conveying capacities. The motor of the rotary feeder, however, is only determined by the dimensioning of the rotary feeder. In a rotary feeder, for example, the motor has for 180 t / h of raw meal the capacity of 5.5 kW, whereby during the operating the capacity of less than 1 kW is received.

Grain destruction: Due to the relative motion of the screw pump the high compression of the bulk solid leads to grain destruction, that should be avoided depending on the industry (for example, alumina industry). KREISEL ceramic rotary feeders cause no appreciable grain destruction.

Motor Control Centre (MCC): Thanks to the small drive motor of the rotary feeder and the smaller pressure generator motor the MCC can be also considerably smaller and therefore more cost-effective performed. These costs may be up to tens of thousands of euros.

Commissioning: As already mentioned in Chapters BULK SOLID PROPERTIES and GRINDING AID, the screw pump reacts to various system parameters. To achieve the correct screw pump configuration during the commissioning, to take into account the points BULK SOLID PROPERTIES and GRINDING AID the multiple modifications are necessary. Screw pitch, plug length, nozzle diameter or return valves adjustment must be determined in time-consuming conversion. The rotary feeder, however, does not respond to these parameters. As usually, a rotary feeder is taken into operation in one or up to two days.

Table 1: Plant data of pneumatic conveying of cement at PPC Hercules.
Plant Data Screw Pump Ceramic Rotary Feeder
Bulk solid [-] Cement Cement
Blaine [m²/g] 3200-5000 3200-5000
Bulk density [kg/dm²] 1150 1150
Raw density [kg/dm²] 3200 3200
Max. conveying distance [m] 260 260
Conveying altitude [m] 55 55
Conveying line diameter [DN] 350 350
Screw pump size [-] 300
Rotary feeder size [-] 700
Motor (installed) [kW] 132 5,5
Bulk solid temperature [°C] 80-110 80-110
Plant altitude [m] 1265 1265
Max. stable conveying capacity [t/h] 100 /130 >175

Space requirement: As a final advantage the low space requirements of the ZSV-H is listed. As you can see on  Fig. 2 and Fig. 4, the ZSV-H can be nearly adapted all too all local conditions. In the case, when a screw pump has found space for installation due to pump surge bin, a rotary feeder can be installed in any case. For example, PPC Hercules builds the screw pump 4,500 mm long. KREISEL Ceramic rotary feeders require only 2,150 mm including motor.

Leckage air: In rotary feeders due to the prevailing pressure differences the leakage air flows arise towards the bulk solid flow. These are between 5% and 12% of the total conveying air quantity. It is discharged via the dust collector. In this example at PPC the leakage air is 6,4 % of the total compressor power. The energy loss by the screw pump nozzle is 15,5%.

Capacity of CERAFEED ZSV-H: The conveying capacity of the ZSV-H is, according to rotary feeder length, between 0.3 up to 250 m³/h. Conveying line pressures up to 2.0 bar can be realized depending on the bulk solid.

5. Energy Balance on PPC Hercules Example

PPC operates various pneumatic conveying systems at the Hercules location. Two of them are used to transport cement from the grinding mill to the receiving silo. The feeding of the cement in the conveying lines was carried out by screw pumps. Repeated disturbances, capacity losses and high energy consumption gave PPC reason to bring about a technical change. PPC targets the cutting edge of the technology – ceramic rotary feeders of KREISEL Germany. Table 1 shows the system parameters of the pneumatic conveying plant with the feeding component Screw pump. The data acquisition shows a max. stable conveying capacity of 100-130 t/h, depending on the type of cement. Besides the insufficient conveying capacity there were the cases of the screw pumps failures because of various reasons. Overfilling and motor failures disturbed the operation.

Table 2: Energy consumption.
Data Screw pump Size 300 Rotary valve Size 700 x 700
Operation time per year [h] 7500 7500
Energy costs [EUR/kWh] 0,08 0,08
Shaft powder requirement of the feeder [kW] 155 5
Shaft powder requirement of the compressor [kW] 336 294
Sum of energy demand [kW] 491 299
Total energy consumption [kWh/year] 3.682.000 2.242.500
Rnrtgy costs per year [EUR] 294.600 179.400
Energy savings per year [kW] 1.440.000
Energy cost savings per year [EUR] 115.200 (-39%)
Return of Investment <3/4 year

In September 2015, the reserve conveying screw pump was replaced by a KREISEL ZSV-H size 700. It was taken into operation within 2 days. During the commissioning, a stable conveying capacity of 140 t/h has revealed. Due to the optimizing the grinding and filter process the plant capacity could be increased to 175 t/h. It was found that the KREISEL ZSV-H has not yet reached its limits. The plant is for four months continuously in operation. Figs. 2a + b above show the plant structure before conversion and after conversion to KREISEL ZSV-H. The inlet was so adjusted, that the support structure could be furthermore used for the supporting the screw pump. This resulted the shortest conversion times. The driving capacity of the rotary feeder is permanently measured by the customer. Due to the special bearings, the rotary feeder is operated with a capacity of less than 1 kW. With the replacement of the screw pump into a ceramic rotary feeder a significant part of the energy costs of pneumatic conveying is saved. As a result, the return on investment amounts to less than 1 year.

6. Summing up

Due to the replacing their screw pump through a KREISEL Ceramic rotary valve PPC was able to increase its cement transport capacity at least to 175 tons per hour. Further advantages are a stable, reliable pneumatic conveying with the lowest energy consumption. An annual energy saving of approx. EUR 100,000 could be achieved. This is one of more than two dozen successful projects with a KREISEL Ceramic rotary feeder. Meanwhile, PPC ordered further ZSV-H for replacement of screw pumps in South Africa. Together with PPC KREISEL is investigating the behavior and life time of the rotary valve. KREISEL is grateful for the excellent and trustful cooperation with PPC and looking forward for more projects in terms of the energy saving.

Page 2 of 2
Similar Companies
more ➥
OZB Özbekoğlu
Frigmaires Engineers
Frigmaires Engineers
Schäffer Verfahrenstechnik GmbH & Co. KG
Schäffer Verfahrenstechnik GmbH & Co. KG
Write the first Comment