Plate And Frame Filter Biology Essay

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Plate and frame filter is commonly known as the press filter, which is probably the most widely used most easily operated device. It is more adaptable to a varied assortment of problems. It's one of the most economical means and provides the most satisfactory results in terms of clarity of a solution. There are different filter cloths to suit different kinds of slurry content.

The aim of the experiment is to evaluate whether the plate and frame filter is able to filter the slurry at a rate of 40L/hr at a concentration of 50kg/cm3 in order to meet the company's needs. The other aim is to find out if the rate of flow will drop relative to the cake accumulation within the filter medium.

Three pressure values which include 0.2, 0.3 and 0.4 bars were tested for the experiment. After the experiment, it was concluded that the 0.3 bar was the ideal pressure for a good performance by the plate and frame filter.

The hypothesis was to prove that when the cake accumulates on the filter medium, it will increase the flow of the resistance. This was proven to be correct after completing the experiment.

Plate and frame filters were also known as pressed filters. When it was first invented in the 1800s, the size was huge. Most importantly, it was difficult to operate due to the inadequacy of yesterday's technology. At that time, the possibilities of modifying the equipment was limited (Sweetland 1914).

In 1927, the filter press happened to be one of the most commonly used filter as it had a simple working principle and the ability to adapt to various assorted problems. When technology improved, Engineers felt that there was a need to re-design plate and frame filter. The manufacturer permitted the engineers to choose parts of the filter that were needed to be modified. As more ideas came into the picture for modification, the plate and frame filter design was upgraded to suit the application (John 1927).

In 1938, modern filters such as vacuum and pressure filters were invented and introduced. In spite of these newer filters, the plate and frame filter was still popular as it was able to recover more solids.Larger cake accumulation will stop filtration cycles and had the ability to achieve efficient washing of the cake to recover valuable products for further processing (Philip1938).

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Figure 1: Olden days filter press (www.water.siemens.com/.../old_press_R.jpg)

1.2 Aim

The aim of the experiment is to evaluate whether the plate and frame filter is able to filter the slurry at a rate of 40L/hr at a concentration of 50kg/cm3 in order to meet the company's needs. The other aim is to determine if the rate of flow will drop relative to the cake accumulation within the filter medium.

1.3 Hypothesis

The hypothesis is that the calcium carbonate slurry production rate is at 40 litres per hour at a concentration of 50 kg/m3. When the cake accumulates on the filter medium, it will increase the flow of the resistance. At a constant applied pressure, the filter medium resistance increases, decreasing the flow rate.

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2. Theory

The process which separates solids from a suspension by means of a porous medium or screen is known as filtration. The filter medium acts as a retainer to retain the solids and steadily forms a cake while the clear filtrate will then be allowed to pass through. When the cake progressively builds up on the medium, it increases the resistance to flow. Under constant applied pressure, the rate of flow will progressively decrease (Singapore Polytechnic 2009).

The process of filtration involves the flow of water through a granular bed, of sand or another suitable media, at a low speed. The media retains most solid matter permitting the water to pass. The process of filtration is usually repetitive to ensure sufficient removal of unwanted particles in the water (Ramstorp 2003).

In a plate and frame filter press, the solid particles are trapped within the frame compartment, between the two filter media held tightly by the plates. When the compartment is almost completely filled with the cake, the operation will be stopped for removal of the cake and subsequent cleanup of the filter unit before the next filtration.

Figure 2: Simple filtration (http://en.wikipedia.org/wiki/Filtration)

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3. Procedure

3.1 Start Up Preparation

Firstly checks were done to ensure that the plates, frames have been stacked properly. The plates and frames were arranged alternatively along the guide beams starting and ending with the 'end plates'. Seven plates and six plates were used in total.12 filter media were inserted between the plate and frames.

Line tracing was also done to trace the flow from the feed tank through the plate and frame filter. The hydraulic valve V1 was closed and then the hydraulic clamp was adjusted using the lever till a hydraulic pressure of 100 bars was achieved.

It was also checked that the drip tray was properly placed at the bottom of the stack of plates and frames after which V5, V6, V7 is closed. The mixing tank T1 was filled with about 3 litres of water for the leak test. Simultaneously valves V2, V3, V4, and V6 were fully open. It was also checked that the filtrate outlet hoses were placed properly in the plastic container.

The power to pump P1 was switched on and the pressure regulator R on the pump was adjusted to a pressure of approximately 0.3 bar. Water was then allowed to pass through the filter (Singapore Polytechnic 2009).

3.2 Leak Testing

After the water is seen leaving through the discharge pipes, the

system was checked for leakage. Pump 1 was then switched off.

If no leakage occurred, the experiment will be carried on to the next phase, if a leakage was present, the hydraulic clamp was released and the alignment of the stacks of plates and frames was checked and leak test carried out again.

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V6 was closed, V7 was opened to drain out the remaining water in the tank T1 and V7 was closed once all the water has been drained from the tank (Singapore Polytechnic 2009).

3.3 Slurry Preparation

The mixing tank T1 was approximately filled with 20 litres of water and 1 kilogram of calcium carbonate was weighed out in a plastic jug. The stirrer of the tank T1 was switched on and one kilogram of calcium carbonate was slowly poured into tank T1 by means of a plastic funnel and the stirrer was left to operate continuously to ensure a uniform feed concentration (Singapore Polytechnic 2009)

3.4 Filtration

Valve V6 was fully opened and the filtrate outlet was placed in a plastic container. After which the pump P1 was started and half a minute was allowed for the flow and the observation of the pressure reading on the pressure gauge PI2.

After which, clear water was poured into tank T1 to rinse the tank while the pump was still running. Thereafter, five litres of water was added to allow it to flush the system and to prevent subsequent chokes (Singapore Polytechnic 2009).

3.5 Clean Up

Pump P1 was then switched off and V6 was closed. Valve V1 was opened to release the hydraulic pump. Then the stacks of plate and frame were dismantled. The filter cakes were scraped off gently from the filter media and the cake was discarded into the plastic container provided. Finally, the equipments, plates, frame and filter media was cleaned and the working area was wiped and dried (Singapore Polytechnic 2009).

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4. Results and Calculation

Number of runs

Pressure at 0.2 bar

Flow rate(L /hour)

Pressure at 0.3 bar

Flow rate (L/hour)

Pressure at 0.4 bar

Flow rate (L/hour)

1

40.8

58.8

110.4

2

45.6

58.8

115.2

3

40.8

61.2

115.2

4

38.4

63.6

115.2

5

40.8

58.8

116.2

6

39.6

61.2

120.0

7

39.6

60.0

118.8

8

39.6

61.2

120.0

Table 1: Volumetric Flow Rate of slurry at a pressure of 0.2, 0.3 and 0.4bar

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4.1 Pressure at 0.2 bar

At 0.2 bar average of volumetric flow rate,

= 40.8+45.6+40.8+38.4+40.8+39.6+39.6+39.6

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= 40.65 L/h

4.2 Pressure at 0.3 bar

At 0.3 bar average of volumetric flow rate,

= 58.8+58.8+61.2+63.6+58.8+61.2+60+61.2

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= 60.45L/hr

4.3 Pressure at 0.3 bar

At 0.4 bar average of volumetric flow rate,

= 110.4+115.2+115.2+115.2+116.2+120+118.8+120

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= 116.38 L/h

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5. Discussion

5.1 Evaluation Of Results

After conducting the experiment it is proven that the filter press has met the capacity requirement of 40L/h. According to the results shown in Table 1, at 0.2bar, the average volumetric flow rate is at 40.5L/h. Therefore the filter press is well suited even when operating at a low pressure. Following the results, at 0.3bar, the average volumetric flow rate is 60.45L/h. Finally, at 0.4 bar, the average volumetric flow rate is 116.4L/h thus, meeting the capacity requirement. And therefore it is then concluded that the filter's optimum operating pressure is at 0.3 bar. Moving on to the turbidity of the filtrate collected, it is shown that the filtrate collected is very clear at the end of the experiment. Hence substantiating that the plate and frame filter matches the requirement of turbidity. Alternatively, to further improve the clarity of the filtrate, more plates could be installed.

5.2 Problems Faced

One of the problems encountered in this experiment is the manual cleaning of the filter. Since cleaning of the filter is time consuming it would be wise to purchase two filter presses. One of the press filters is used to cope with the down time for cleaning the filter. The other filter would act as a standby filter, in cases whereby the filter has to be sent for servicing or maintenance purposes. Second problem faced was the leakage in between the plate and frame filter. If the medium used was corrosive it might cause harmful effect to not only the people but also to the environment.

5.3 Modifications To Be Made

Like every other experiment; this experiment too has its own flaws. This plate and frame system has a regulator at the back of the pump.

So as to constantly monitor the output pressure of the pump a

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technician is required to adjust the regulator at the back of the pump.

So as to alter the flaw of the system, it has been decided that modification of the system has to be done. To measure the differential pressure across the filter, a pressure differential gauge has to be added.

There will be a need to switch over the slurry to a standby filter when the differential pressure increases. After which the filter cake from the filter plate and filter cloth can be washed off.

To prevent a technician to constantly monitor the system a control valve and a flow meter have also been added in the system. The flow rate can then be monitored by the Distributed Control System (DCS) system. As for the pump, an addition of another pump should be installed. Maintenance will be made easier when the pump is down. Moreover it will not affect the filtering processes as the pump acts as a standby pump.

6. Conclusion

The aim of the experiment has also been met in that; the flowrate will drop relative to the cake accumulation within the filter medium.

The hypothesis is also proven to be correct seeing that the plate and frame filter is able to filter the slurry at a rate of 40L/hr at a concentration of 50kg/cm3.

It is also finally concluded that 0.3 bar is the most ideal pressure for the operation of the plate and frame filter.

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