Pr/paper/flyashdisposal-powertrends2000

HIGH DENSITY ASH SLURRY PUMPING

AND DISPOSAL:

An Environmentally Safe and Economical Alternative

Berry van den Broek

Manager Business Development

GEHO PUMPS

Venlo, the Netherlands

Phone: (+31)77-3895200, telefax: (+31)77-3824844

e-mail: envirotech@envirotech.nl, website: http://www.envirotech.nl

CONTENTS

1 Company Introduction

2 Conventional Ash Disposal Systems

System Description

Drawbacks

3 High Density Slurry Transportation and Disposal Systems

System Description

Disposal Site

Technical Features

Sloped Disposal Site Operating Parameters

Slurry Quality

Deposit Management

4. Typical Operational Questions

Winter Conditions

Hardening of Slurry

Pipeline Flushing

Energy Consumption

Labour Requirement

Reliability

5. Project Organisation

6. Specific Advantages of the Proposed GEHO System

Ecological Advantages

Operational Advantages

Financial Advantages

7. GEHO Piston Diaphragm Pumps

Technical Features

Typical applications in the Power Industry
Fig.1 GEHO piston diaphragm pump.

1. COMPANY INTRODUCTION

GEHO PUMPS, established

in 1916, is specialized in the

design, development and

manufacture of high pressure

slurry pumps. In the 50's

GEHO PUMPS started with

the manufacture of crankshaft

driven piston pumps up to

approximately 20 kW,

handling lightly abrasive,

contaminated water and

sludges. The increasing

demand from the general

industry directed GEHO

PUMPS to the development

of higher power rated machines up to a 1,500 kW level. In addition, the requirement for

economical, cost effective handling of extremely abrasive slurries, directed GEHO PUMPS

simultaneously to the development of the piston diaphragm pump design. This diaphragm pump

features a diaphragm construction, that separates the pump’s wear sensitive parts (piston, liner,

etc.) from the abrasive slurry to be pumped. These parts now operate in a clean hydraulic oil, as

the flexible rubber diaphragm ensures a continuous mechanical separation. (Fig. 1) The first

diaphragm pumps were introduced in the late 60's. Since then they have been included in

numerous pumping projects where abrasive slurries have to be pumped against high discharge

pressures.

Some typical references include:

• Pumping highly abrasive red mud tailingsin the alumina industry atsolids concentrations of

50-65% by weight (2-5 miles) (Canada, Australia, Yugoslavia).

• Pumping abrasive iron sands through a 12 miles long pipeline in New Zealand, 60-65% by

weight and through a 60 miles long pipeline in China.

• Pumping high density coal slurries (70% by weight) into gasifiers for coal gasification

(Texaco process).

• Pumping of high density fly ash slurries through a 6 mile pipeline in Australia.

Further references include pumping several different mine tailings, ore concentrates, sewage

sludges, shell sands and other highly abrasive slurries.

GEHO PUMPS, whose headquarters are located in Venlo, the Netherlands, have the most

modern manufacturing facilities. It operates the world's largest slurry pump test facility with an

installed motor power of up to 1,500 kW to enable testing all pumps at full load conditions prior

to shipment. Laboratory facilities are available to do all basic slurry analysis as well as to carry

out small to full scale slurry pumping tests.

Power plants firing coal produce, due to theirsizes, considerable amounts ofsolid waste: fly ash

and bottom ash. These are often referred to as Coal Combustion Residues (CCR). Fly ash is

mostly collected in the fluegas cleaning systems (such as with electrostatic precipitators etc.)

From there it is pneumatically transported over a relatively short distance (on the plant site) to

temporary storage silos. Bottom ash is generally collected directly underneath the boiler.
dilute residue

coarse

contamination

synthetical seal

high

pressure

water

return

fine

dust

Fig. 2 Wet disposal site.

These hotslagsimmediately are cooled down with water and transported with chain conveyors or

similar methods. From the temporary storage facilities the CCR needs to be transported to a

disposalsite or the CCR may be used asfeedstock in for example the cement or road construction

industry.

Lean phase slurry systems have been used for many years at a number of power stations to

transport and dispose the CCR. The lean phase slurry systems are associated with high running

costs, high water throughput and environmental concerns. Therefore the performance of a

number of alternative ash collection and disposal systems are presently being investigated

worldwide. Recent advances in dense phase slurry pumping systems offer advantages for ash

disposal systems by virtue of reducing land and water utilization, and by reducing capital and

operating costs.

Many existing ash dam disposal sites for both bottom and fly ash are considered to be both

economically and environmentally unsatisfactory. These present disposalsites are either an open

disposal system where the excess water from the ash dam is returned to the environment or a

closed system where the water isrecycled. Such return water pipesfrom the ash dam to the power

plant often require chemical cleaning, due to scaling, after only a couple of years of service.

Alternative "dry" disposal systems, where the ashes are only wetted (15-20 percent water

content), are also expensive to operate and maintain due to the high costs of truck transport.

The produced quantities of CCR are of course largely depending on the quality of coal fired.

2. CONVENTIONAL ASH DISPOSAL SYSTEMS

System description

When burning coal, power plants produce enormous quantities of waste (fly ash, bottom ash etc.)

which needs to be disposed of, in an environmentally safe manner at the lowest possible costs.

The conventional way of disposing

is pumping ash slurries through a

pipeline to a holding pond. The

solids concentration made up,

before introducing to a pump

system, is generally about 7-15% by

weight. Thisis about the maximum,

that conventional centrifugal pumps

(dredge type pumps) can handle to

transport the slurry over a longer

distance. As the slurry has a dilute,

water like character it has to be disposed of in ponds.

The disposal is characterised by a "beach" area of wet, settled solids, and a pond of separated

water (Fig. 2). This "beach" is characterised by a low slope (< 0.5%). At the interface with the

water pond, the slope increases rapidly under water as solids settle in the dilute suspension.

Ash storage must be contained in a void, or in a carefully constructed dam. Water volumes are

high, the water becomes saturated with leached salts and must be recirculated. The disposed

slurry is allowed to settle as much as possible and the over-flow water is either returned to the

plant or treated and discharged. Due to the low concentration, the settled material however will

never reach a solid consistency.
Fig. 3 Typical layout of high density ash

slurry pumping station.

1. Slurry tank, 2. Booster pumps, 3. Lobster

pot, 4. Sieve, 5. Suction dampeners, 6.

GEHO pump.

Drawbacks

The low density hydraulic disposal is a costly operation due to such factors as:

A. High capital costs are required for the initial design and construction of the lagoon and dams.

B. Power consumption of the pump station is high, as enormous quantities of water have to be

pumped and possibly returned. In addition, centrifugal pumps operate at low efficiencies(50-

55% only).

C. Although the solids concentration islow, maintenance coststo the centrifugal pumps are very

high. The abrasive character of the ash causes excessive wear to the relatively high speed

centrifugal pumps. The high maintenance costs are caused by both parts consumption as well

as maintenance labour hours.

D. The low density slurry often creates a fast scaling on the inside of the pipeline. As a result

approximately 1 to 2 times a year the entire pipeline hasto be disassembled and either turned

or even fully cleaned, which is a time consuming and costly operation.

Apart from these financial drawbacks, also environmentally it should be recognized, that the

pond itself, with itssettled solids, does generally not allow for reuse later. Solids deposited in this

regime consolidate to a maximum settled concentration depending on the characteristics of the

solids, and the compaction caused by the weight of accumulated solids. However, because of the

high water load in the deposit and the depth ofsaturated solids bed, the deposit remains "wet" for

many years after disposal is completed, and this hinders the rehabilitation of the site. There are

designs to speed drainage once deposition is completed, however these offer only a modest

increase in the deposit drying rate. If the over-flow water has to be discharged, it will be a costly

treatment to clean it up.

Alternative "dry" disposalsystems, where ashes are wetted only (15-20% water content), are also

expensive to operate and maintain due to the high costs of truck or belt transport. In addition,

mechanical spreading of the ashes on the disposal site with help of machines is required.

3. HIGH DENSITY SLURRY TRANSPORTATION AND DISPOSAL

SYSTEMS

The drawbacks of the Wet Ash Disposal Systems can

be overcome with the High Density Slurry

Transportation and Disposal Systems. The aim of

thistechnology isto prepare slurry at a concentration

where it behaves as a viscous fluid which will

distribute over the disposal site by gravity flow, but

from which, because of the concentration, there is

none or very little water runoff to form a pond.

System Description

GEHO PUMPS proposes a unique technology for the

transportation of the Coal Combustion Residues at

power plants. This technology is based on high

density slurry transportation and disposal as is

commonly used in the mining and mineral processing

industry (i.e. at alumina refineries).
stabilizing layer -0,30 m

fly ash

mineral sealing layer drainage layer

Fig. 4 High density ash slurry disposal site.

The slurry is prepared from a mixture of water, with the silo stored fly ash, bottom ash, and

sometimes flue gas desulphurisation gypsum and additives (as required). The high density

mixture is prepared in either a batch-type or continuous mixer.

The slurry from the mixer is discharged into the slurry tank (Fig.3), which allowsfor a minimum

residence time. The slurry content of the tank is continuously agitated to maintain a homogeneous

mixture. The GEHO Piston Diaphragm Pump takes its suction from this tank and transports the

high density slurry to the disposal area. The pump is driven by a variable speed motor, controlled

by the slurry tank level. The slurry consistency is verified by a density measurement in the

suction line plus a pressure drop measurement in the discharge line immediately downstream of

the pump. These signals can be used to re-adjust the mixing ratios.

The solids concentration is carefully controlled, as it should be as high as possible, to reduce

required water quantities, howevershould also be kept under a typical maximum. Above a certain

solids concentration the ash slurry tendsto suddenly increase in viscosity, as a result of which the

friction loss in the discharge pipeline increases dramatically. As all ash slurries are different this

"critical" concentration varies, however it will be in the range of 55-75%. Staying slightly under

this "critical" concentration loss (i.e. reasonable power consumption) is essential.

The resulting rheological behaviour is

completely different from the low

density ash disposal systems. The

produced slurry is (almost)

homogeneous and viscous. The slurry

discharged as such has a

homogeneous, more viscous

character. As a result its flowing

character, when compared to low

density disposal, is substantially

reduced. For that reason a solid,

expensive pond construction, like in

the case of low density disposal, is

absolutely not required (Fig. 4).

Disposal Site

When disposing an ash slurry just below its "critical" concentration in a pond, it will separate

hardly any or no water. It is therefor often referred to as "Dry Stacking".

The slurry is distributed in thin (approx. 100 mm thick) layers promoting rapid moisture loss by

evaporation. This ensures that the solids rapidly consolidate to a high density, forming a deposit

which hassufficient bearing strength to support machinery used to progressively rehabilitate the

site as it is filled. The dry stacking is easier of course, where solar drying is better available.

During drying time the discharge of the slurry can be removed to another discharge point at the

lagoon through a ring line/distribution line system. Salts in the deposit form a thin crystalline

layer on the surface which binds the fine solids particles, preventing dusting. The deposit slope

forms at 3-6%, providing a surface which will discharge rainfall at a non erosive velocity. It is

therefor also referred to as "Sloped Disposal".

The consolidated deposit has a low permeability. Salts retained in the deposit when water is lost

by evaporation are locked into the deposit, minimising the risk of leaching, and associated

contamination of associated ground water. Such systems are frequently and successfully used in

the alumina industry, disposing red mud tailings, and mining and mineral processing industries.
Technical Features

Many features of this system can be mentioned:

A. Low initial pond costs as the introduced tailings slurry has a much stronger consistency,

eliminating the need for a strong dam construction. In addition, the introduced flow rate is

reduced to a minimum (more solids instead of water), for which reason the size of the pond

can be minimized. This also applies to the size of the discharge pipeline.

B. Power costs savings can be realized as a result of the strongly reduced flow rates as well as

the high efficiencies of the GEHO Piston Diaphragm Pumps(up to 93%). This efficiencywill

not change over the service life of the pump.

C. No need for an over-flow water return line system, eliminating maintenance and power

consumption for this system.

D. Due to the high solids concentration it is experienced and proven that the scaling effect in the

discharge line is almost eliminated. Therefore the need for turning a discharge line or

disassembling and cleaning is eliminated.

E. The consistency of the ash slurry allows for an underground mine backfill operation, where

possible. It eliminates the disposal on surface and contributes to the stability of the

underground mine.

F. The use of the GEHO piston diaphragm pump for this application eliminates almost all

maintenance to the pump station. The pump, designed for handling abrasive slurries, allows

for a guaranteed availability, of over 98% with scheduled short maintenance stops

approximately every 10-15 weeks. The rest of the time being in continuous 24 h/day service,

if required. Maintenance and operator costs are substantially reduced when compared to the

low density system.

Sloped Disposal Site Operating Parameters

The aim of a sloped disposal site operation is threefold:

1. Solids should be distributed over the site with a minimum of operator intervention.

2. Solids should consolidate by drying.

3. Water (or slurry) accumulation at the toe of the deposit should be minimised.

To achieve these aims the slurry quality must be controlled, and the deposit must be managed.

Slurry Quality

The slurry behaviour in the pipeline as well as on the disposal site is dictated by the same

parameters: the yield stress and viscosity of the slurry. Most ash slurries of high solids

concentration behave according the Bingham plastic or yield pseudo-plastic rheology principles.

When the ash slurry is self hardening (f.e. due to high calcium content) the element of time

becomes important, possibly to the effect that residence times in the installation must be

shortened and velocities in the pipeline increased.

Slurry quality, principally its concentration to achieve a rheology where the slurry will flow as a

relatively homogeneousfluid with minimum of waterseparation, must be controlled at the slurry

preparation plant. If the slurry istoo "thin", the slurry runstoo freely over the deposit at relatively

high velocity. This causes erosion of the deposit, and a pond forms at the toe of the deposit.

Channels eroded in the deposit promote further erosion from rainfall, resulting in a gradual

deterioration of the deposit and conversion from a "sloped" disposal site to a "pond" site.

Deposit Management

The sloped deposit must be managed to achieve a relatively uniform distribution across the site,

and to achieve the deposit drying and consolidation aims. This principally involves the

management of slurry discharge spigots to distribute slurry over the site at a rate which is
consistent with the prevailing site conditions. This includes:

Χ Management of the number of locations of the discharge spigots.

The design requires slurry to be discharged from a number of discharge spigots arranged

along one edge of the active void. The spigots are located at intervals, and it is planned that

discharge will be from every other spigot. The flow of slurry across the site is a function of

the discharge rate from a spigot, the condition of the underlying deposit, and the slurry

concentration and rheology. If the discharge rate is too high (say for example that all the

slurry was discharged from the header pipe), experience hasshown that flow tendsto channel

at relatively high velocity, resulting in poor distribution, and ponding at the toe of the deposit.

Conversely if the flow is too low, moisture loss, both by evaporation and to the deposit,

causes the slurry concentration to increase too rapidly, and slurry will not flow over the

deposit. This result is similar to the effects observed when the slurry concentration is either

too low, or too high. The number of spigots actually used on the site at any time will be

determined from experience, and will be appropriate to the slurry properties, the pipeline flow

rate, the frequency of pipeline shutdown, and the prevailing environmental conditions.

After slurry has been discharged from a spigot for some time, a condition will be reached

where slurry flowing from the spigot can no longer distribute and dry across the surface

created during its period of operation. Thisis generally evidenced by slurry pondsforming at

the toe of the deposit. When this occurs, flow must be switched to an alternate spigot. The

frequency will vary with total deposition rate, the development of the deposit, and the

environmental conditions.

Χ Environmental Conditions

The sloped disposal design concept is based on the deposited solids being consolidated by

water loss through evaporation. Evaporation rates are controlled by:

. the daily sunlight hours

. wind

. slurry conditions.

While there is sufficient water in the slurry for the surface to be maintained wet by capillary

rise, the evaporation rate is equivalent to the prevailing free surface evaporation at the site.

Once moisture levels fall and capillary rise no longer occurs, moisture loss is controlled by

more complex mechanisms, and the rate of loss rapidly falls. Surface cracking caused by

depositshrinkage on drying can open a surface to the bottom of a slurry layer, and increase the

evaporation rate.

Clearly, to manage the deposit it will be necessary to provide additional area on the disposal site

during the initial development (when the full area of the deposit slope has not been developed),

and during winter, when the low drying rates will require the area to be increased by 200-300% to

dispose of the same mass of water as would be evaporated during summer.

4. TYPICAL OPERATIONAL QUESTIONS

Winter Conditions

On many possible locations where such CCR Transportation and Disposal Installations may find

acceptance, winters can be cold with temperatures below 0°C for longer periods of time.

Although there is a heat generation in the pipeline due to friction and there is a limited residence

time of the slurry in the pipeline it may be required to protect the slurry pipeline from freezing.

There are several ways of protection:
1. Underground Pipeline:

At sufficient depth (in Middle of Europe: say 1 meter) the temperature will not drop below

0°C. An underground pipeline will therefore not freeze. Additional advantages are (1) that

there is also less thermal expansion in summertime, (2) that the pipeline is invisible and (3)

that there are no crossings with roads or railways.

2. Thermal Isolation of the Pipeline:

Depending on the prevailing winter conditions, it may suffice to have a thermal isolation with

protection against damage around the pipe. The advantage of thissolution isthat the pipeline

remains easily accessible.

3. Thermal Isolation with Heating (Tracing) of the Pipeline:

When winter conditions are more severe electrical heating elements may be required.

All three solutions have proven to be working to full satisfaction.

Hardening of Slurry

High amounts of CaO or other chemicals in the slurry may result in quicker hardening of the

slurry with the possibility of pipeline blockages.

During the design stage of the installation this chemical behaviour needs to be researched. Such

research will result in a hardening time of the slurry. The residence time in the entire installation

(mixer, slurry tank and pipeline) needs to be shorter than this hardening time. This, again, may

have an influence on the pipeline diameterselection. Alternatively a higher water content may be

selected to maintain a sufficiently low viscosity in the pipeline and on the disposal area.

It is obviousthatspecial requirements on the pipeline diameter and on the water of the slurrywill

have an impact on the pipeline pressure losses and rheological behaviour of the slurry.

Pipeline Flushing

It isimportant to clean (flush) the pipeline on a regular basis and prior to a majorshut down. The

cleaning is very easy and is generally done with water. To increase the cleaning results, "pigging"

isrecommended. In that case cleaning balls(so-called "pigs") are introduced to the pipeline with

help of pigging stations. These cleaning balls are moved through the pipeline bywater. The water

pressure can be generated by the GEHO Piston Diaphragm Pumps. In case an amount (of water

of the content of the pipeline) isrun through the system, an additional volume of water will be let

onto the disposal area, which will be drained from the disposalsite in the same way asrainwater.

This amount of water can be considered minimum, compared to a short rain shower. For

example: the content of a pipeline of 150 mm and 3 km length is 53 m

3

, spread over an area of

200 x 200 m this is only 1.3 mm. If pigging is done at a speed of 1 m/s, a 3 km pipeline is

cleaned in 50 minutes.

Energy Consumption

The energy consumers are all located at the installation i.e. at the power plant. There are no

consumers on the disposal area (as no mechanical spreading is required). The total energy

consumption of the entire transportation and disposal system is therefor very low. A quantity of

100 t/h of dry ashes, (this is approx. 100 m

3

at 65 % solids concentration) pumped through a

pipeline at 60 bar, requires approx. 185 kW. A booster pump and agitator may consume another

50 kW. Total 235 kW.

Labour Requirements

Once the installation is properly installed and commissioned, it will run fully automatically and

can be controlled from the power plant's Central Control Room. The proposed installation does

not require any additional operating personnel.
With respect to maintenance requirements, it can be stated that the design of the installation is

based on rigid and wear resistant components reducing labour requirements to a minimum. It is

estimated that annual labour requirements for maintenance is limited to approx. 250 hours.

Reliability

The proposed installation is based on a combination of proven technologies: high density slurry

pumping with piston diaphragm pumps, including slurry preparation and mineral waste disposal.

Although the GEHO Piston Diaphragm Pumps have a guaranteed availability of 98 %, standby

equipment is included in the design. Further all equipment is amply sized with adequate safety

margins with respect to capacities, as well as operating conditions, if considered necessary all can

include with adequate standby.

5. PROJECT ORGANISATION

In all details GEHO PUMPS is organised to adequately manufacture and supply specialty pumps

to the power industries. They are in the position to support the sales activities by carrying out

extensive slurry rheology lab testing, by the supply of basic pipeline engineering and basic pump

station engineering. In most projects GEHO PUMPS will cooperate with reputable partners and

contractors for the supply of turn-key deliveries. These partners have experience in project

management, civil engineering, detailed pipeline and pump station engineering, disposal site

engineering etc. GEHO PUMPS is free to select those partners who are most appropriate for the

particular project.

6. SPECIFIC ADVANTAGES OF THE PROPOSED SYSTEM

For somewhat more than 10 years it has been possible to transport high density slurries

(practically without free water) through a long distance pipeline. Subsequently it is possible to

dispose (waste) slurry in an environmentally safe and sound way. These possibilities became

economically viable through the development of high pressure piston diaphragm pumps.

Compared with the conventional ways of transportation by means of conveyor belts, trucks or

low density slurry pumping, this proposed technology offers following:

Environmental advantages

1. No ground water pollution because of the solidification of the slurry on the disposal site.

2. No dusting because of slurry solidification.

3. Easy drainage of rainwater.

4. Hills can be easily constructed in order to re-create the original landscape.

5. Possibility of recultivation/revegetation.

6. No noise on the transportation track or in the disposal site.

7. No spoilage and clean transportation track due to a fully enclosed pipeline system.

8. No dirty exhaust gases from trucks on the transportation track or at the disposal site.

9. The pipeline can be buried underground and remains invisible.

10. No topographic limitations to the pipeline systems.
Fig. 5 GEHO piston diaphragm pump.

Operational advantages

1. The slurry preparation, transportation and disposal is completely automated. The entire system

can be operated and controlled at one location. This location can be the power plant's Central

Control Room. Thus no additional manpower isrequired. (The proposed system providesfor a

local control room for maintenance, start-up, purposes etc.)

2. The slurry preparation, transportation and disposal is continuous and trouble free.

3. The system is not influenced by weather conditions(low temperatures,storms, heavy rainfalls

etc.)

4. No additional manpower or machinery is required to spread the waste over the whole area of

the disposal site.

5. Therefor no accommodations for personnel or equipment on the disposal site are required.

6. Flexibility: a later change of the pipeline routing is possible at low costs.

7. The pipeline system provides adequate standby facility and allowsfor more freedom of layout

(routing).

8. The installation offers high availability and reliability in summer as well asin winterseasons.

9. The installation requires little maintenance.

10. Easy cleaning possibilities of installation and pipeline.

Financial advantages

1. The pump system is designed to operate 25-30 years, thusreducing the depreciation per year.

2. The energy consumption of the entire pumping system will generally be lower.

3. The expensive operating costs (high spare parts consumption and labour) of trucks and belts

is eliminated.

4. No roads for trucks or observation roads for conveyor belts are to be constructed and

maintained.

5. Costly cleaning of trucks or conveyor belts is eliminated.

6. A separate service crew (for cleaning and repair) for trucks or belts is not necessary, neither

are truck drivers.

7. No energy consumers (infrastructure!) on the disposal site.

In short, the proposed system is proven technology, ecological preferable and certainly reduce the

total operating and investment costs.

7. THE GEHO PISTON DIAPHRAGM PUMP

Technical Features

This diaphragm pump, derived from a

conventional piston pumps but

features a diaphragm construction, that

separates the pump running parts

(piston, liner, etc.) from the abrasive

slurry to be pumped. The running parts

operate in a clean hydraulic oil and the

flexible rubber diaphragm ensures a

continuous mechanical separation.

(Fig. 5)

The most important consideration

regarding the piston diaphragm pump

is to avoid failure of the diaphragm.
Fig. 7 High pressure cone valve.

The amount of propelling liquid volume can change through leakages at the piston and/or the

stuffing box packing. A reduction of the volume of propelling liquid can lead to diaphragm

damage through constant striking against the rear wall. On the contrary, should an overfilling of

the volume of propelling liquid arise, the diaphragm will become overstretched and, after a

period of time, will be forced into the discharge bore.

To cope with these problems, the design of GEHO piston diaphragm pump features a unique

system for keeping the propelling liquid amount between piston and diaphragm constant. This

serves to maintain the optimal travelling position for the diaphragm (Fig. 6). The system uses

contactless electricalswitchesto monitor the diaphragm position, which actuatesfilling or outlet

valves for the propelling liquid, as required. In addition to this standard proven concept GEHO

PUMPS designed a unique modification to this system, for which worldwide patent is pending.

The modified system can cope with all variations in operating data. The system calculates the

required filling and outlet times based on pressure signals, speed signals, acceleration and

deceleration signals. The central processing unit, with memory, keeps the important operating

data for later diagnosis of pump condition and self diagnostics.

In the piston diaphragm pump the valve

components are the only wearing parts. The

diaphragm is recommended to be changed once

a year for preventive maintenance. To keep the

down time as short as possible, GEHO PUMPS

supplies its larger pumps standard with a

hydraulic system for opening the valve covers

and the rapid replacement of the valve seat (Fig.

7). This hydraulic system permits fast and

reliable dismantling and assembly with

minimum physical effort. A special valve and

cylinder cover design permits uniform

tightening, of all bolts with the prescribed

tension, without effort. The piston ring pressure

areas are interconnected by channels inside the cover. Oil pressure is applied to the pressure

piston of each stud and follower, the nuts are then locked by hand. For the purpose of dismantling

the valve seat, pressurised oil is forced between the outer face of the conical seat and the valve

box casing. The shrink fit is thereby released and the valve seat freed. The time required for the

replacement of one complete valve is at the most 30 minutes, and 20 minutes for the valve

components.

Hydraulic tools are also used for piston fitting and removal on duplex pumps and for the fitting

and removal of all drive end bearings. This system is of particular importance where large pump

installations are concerned. GEHO PUMPS were the first to use this system on slurry pumps.

Applications in the Power Industry

Coal slurry pipeline transportation

A slurry pipeline is an efficient means of transporting solidssafely,silently and reliably over long

distances. It is a proven, environmentally safe technology and a viable alternative to railroad and

truck hauling. Climatic and terrain conditions may be so severe that there is no alternative to a

pipeline. Pipeline economics dictate that the slurry is highly concentrated and that it is

consequently pumped through the pipeline with the aid of positive displacement pumps.
Piston diaphragm pumps have, because of lower wear substantially lower operating costs,

become the pump of choice over plunger and piston pumps. The economic balance of capital

costs against operating costs, favors piston diaphragm pumps on applications where the slurry is

abrasive of where pressures are high. Depending on the mode of the pipeline operation, the

extremely high availability of GEHO piston diaphragm pumps obviates the need for a standby

pump, thus reducing capital investment. Numerous slurry pipelines world-wide rely on GEHO

heavy duty pumps. The high availability and cost effectiveness of the pumpsis unmatched and is

demonstrated by the handling of most diverse slurries such as coal, nickel, iron and phosphate

concentrates, fly ash, sewage sludges, red mud and other tailings.

Coal gasification

World-wide, most gasification plants using the TEXACO process, employ GEHO piston

diaphragm pumps for transferring coal slurry and feeding gasifiers. Meeting the most stringent

performance requirements, they handle coal pastes of up to 70% solids content.

Fluidized bed combustion

GEHO PUMPS supplies proven pumping systemsfor the feeding of atmospheric and pressurized

fluidized bed combustion systems with coal pastes of up to 80% solids content.

Ash disposal

All kinds of ash slurries can be handled in a dilute, dense of very paste form, thus avoiding large

tailings dams. Water usage is reduced to a minimum.