Resource Recovery Transfer Stations – Design & Operating ...€¦ ·...

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WasteMINZ Annual Conference

Claudelands, Hamilton, New Zealand 17-19 October 2012

Resource Recovery Transfer Stations – Design

& Operating Principles Geoff Thompson

Sinclair Knight Merz Pty Limited Environment and Infrastructure Consultants

Phone +61 7 3026 8033 INTRODUCTION As is the case for the development of any project, the planning and design stage of a waste transfer station has the most influence over its ultimate success. Probably the two earliest facility planning decisions to be made are its location and the types of wastes it will receive. Having made those fundamental decisions, four key choices about the operation of the transfer station will largely determine its final form:

Resource recovery – What is to be recovered? How? Where within the facility will recovery occur?

Safety – How to manage the risk of users falling from height into bins and pits and keep users and waste separate. Other safety issues must be considered but this one has the most influence over the final form of this station.

Handling and load out of residual waste – Fixed versus mobile plant? Degree of compaction required? Number of supervisory staff? Importance of load-out speed?

Mode of residual waste transport – How far to disposal point? Need for unloading equipment? Time taken to unload? Payload capacity?

Until the ideal of zero or near-zero waste is achieved, the final two matters, and especially the last (residual waste transport mode) will significantly influence the whole of life economics of a transfer station project. Generally this choice has the greatest impact on the most expensive phase of the project – operation. The following attempts to set out the pros and cons of the various options within each of the above four fundamental planning parameters.


RESOURCE RECOVERY PHILOSOPHY What to recover? Only high value items eg metals Lower operations cost

Reduced impact of resource recovery and waste minimisation message.

Recover everything possible Highest recovery of resources

Higher operations cost

How to recover? Passive drop off by customer

Lower operations cost Lower recovery of resources Contamination of materials unless supervised

Active recovery from customer by site staff

Highest recovery of resources Least effort for customer Higher operations cost


Where to recover? Before pay point (gatehouse)

Strongest waste reduction message Extra supervision to prevent deposit of residual

waste

After pay point

Long term fee setting flexibility Even users with no residual waste must use

gatehouse

At residuals drop off location

Lower capital cost (no need for separate facility) Lower operating cost (share supervision with

residuals drop off zone) Lower recovery of resources

Before residuals drop off location

Better recovery of resources Higher capital and operating costs


SAFETY - FALLS FROM HEIGHTS AND USER/WASTE SEPARATION There are other safety issues to be managed at transfer stations, but guarding against users falling into residual waste push pits/bins and separating users from waste material can have expensive implications for the ongoing costs of handling residual waste materials. Larger Stations – users include tipping vehicles

Push pit (deep)

Quick and well defined separation of waste from user.

Fall protection along edge can result in hand and/or lifting injuries

Flat floor

No falls from height Less waste/user separation requires more

supervision

Smaller stations – users unload by hand

Open top bins

Quick and well defined separation of waste from user.

Fall protection barriers can result in hand and/or lifting injuries

Push pit (shallow)

No falls from height Quick and well defined separation of waste from

user.


Tipping bucket

No falls from height Quick and well defined separation of waste from

user. If tipping bucket breaks down, a replacement

cannot be borrowed/hired and fitted quickly. Therefore, need a contingency plan which uses an alternative system

Slower movement of waste from customer to bin/pit


HANDLING AND LOAD OUT OF RESIDUAL WASTE Handling = Moving residual waste from point of deposit to point of load out. No Handling Direct deposit into transfer container/truck

Low capital cost Limited compaction possible No storage other than transfer container

capacity No chance for last minute resource recovery

once in container Not suitable for large vehicle customers

Handling between points of deposit and load out via mobile plant

Deep push pit

Compaction Storage

Less supervision of traffic required

Higher capital cost (retaining walls) No chance for last minute resource recovery

once in pit


Shallow push pit

Last minute resource recovery possible Some in-pit compaction Some in-pit storage Less supervision of traffic required Medium capital cost

Flat floor

Last minute resource recovery possible Lower capital cost Compaction Storage More supervision of traffic required Better suited to users with tipping vehicles

than hand unloaders

Handling between points of deposit and load out via fixed plant Conveyor

Mobile loader not required If conveyor breaks down, a replacement

cannot be borrowed/hired and fitted quickly. Therefore, need a contingency plan which uses an alternative handling system

Walking Floor

Mobile loader not required If walking floor breaks down, a replacement

cannot be borrowed/hired and fitted quickly. Therefore, need a contingency plan which uses an alternative handling system


Loading of Transfer Trucks Top load – direct

Fast load out Higher capital cost (higher retaining walls

required)

Top load – push wall

Medium load out speed

Medium capital cost (lower retaining walls required)

Stationary compactor

Can reduce need for mobile plant when part of a push pit or flat floor system (only the loader function is required, not compaction)

Strong (heavy) container needed to withstand compactor force. Therefore, lesser waste payload

If compactor breaks down, a replacement cannot be borrowed/hired and fitted quickly. Therefore, need a contingency plan which uses an alternative loading system


Slug packer

Can reduce need for mobile plant when part of a push pit or flat floor system (only the loader function is required, not compaction)

Pre compaction means container can be of lower strength and lighter (aluminium). Higher payload of waste

High capital cost of slug packer If slug packer breaks down a replacement

cannot be borrowed/hired and fitted quickly. Therefore, need a contingency plan which uses an alternative loading system.

Baling

Allow uses of lower cost, flat top transfer trucks Less/no compaction required at landfill Less litter at landfill because bales are tied

Capital and operating costs of baling equipment Additional floor area required for loading of bales

onto truck If baling equipment breaks down, a replacement

cannot be borrowed/hired and fitted quickly. Therefore, need a contingency plan which uses an alternative loading system.


RESIDUAL WASTE TRANSPORT

Open-top bins (hook-lift, roll-on roll-off)

Lower capital cost Self unloading

Lower pay loads (3-15t)

Flat bed truck to carry baled waste

Lower capital cost Larger pay loads

Unloading plant required Slower unloading

Semi trailer (tipper) Fastest unload Larger pay loads (20t) Self unloading (note risk of hang-ups)

Medium capital cost Stability while unloading

Semi trailer (walking floor)

Larger payloads (steel body 20 tonne; aluminium body 25 tonne)

Self unloading Higher capital cost

B-Doubles

Same length as semi trailer but more axles to share load. Therefore, larger payloads (30-44t)

Mini B-double can unload by tipping due to smaller trailer size

Special measures such as shredding are likely to be required to fully exploit available payload (weight)

Difficult to unload both containers without unhitching rear trailer. Therefore, slower unloading

Higher capital cost.


A-Doubles or Road Trains

Highest truck payloads (45-55t in two trailer form)

Need walking floor to unload safely Discharge each trailer separately. Therefore,

slower unloading Generally not allowed on urban roads and many

non-urban roads High capital cost

Rail

Largest payload (1000t) Must rehandle waste containers onto trucks to

unload at landfill. Separate rail to road inter-modal facility required.

Special unloading equipment required to unload waste containers.

Highest capital and operating costs (train, rail infrastructure, inter-modal and unloading)

Need large waste throughput to fill train quickly. Otherwise odour etc impacts of aging waste.


CONCLUSIONS Four key planning aspects of a transfer station will largely dictate its final form and operational success:

Resource recovery philosophy

Safety

Handling and load-out of residual waste

Mode of transporting residual waste off site. While the above tabulation should assist transfer station proponents to plan such facilities, it can be seen that there is no clear answer for some of the choices required. Many issues require a trade-off between competing priorities including the familiar one of capital versus operating funds availability. For all systems, other than those with a low percentage of residual waste or a very short distance to disposal location, the highest system cost component is the haul of residuals to disposal location. The larger the quantity of residual wastes and the longer the haul to the location of residuals disposal, then the greater will be the whole of life economic benefit of investing capital up front to improve transport efficiencies and to a lesser extent, residuals handling and load out. Such efficiencies come from getting as much material on the transfer truck/train/ship as possible. Within a class of transport – say trucks for example – the transport operating costs vary little with weight carried. These costs are closely related to hours of vehicle operation. For the usual example of transfer by truck, the cost of wages, insurance, vehicle registration etc are largely independent of payload. Fuel and servicing are influenced to a small degree by payload but are far more related to the number of hours of operation. The very strong influence of residual waste transfer on system economics will reduce as its quantity reduces.

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