Optimization Process
The following building blocks illustrate the processes in system optimization:
The following table illustrates typical activities in the zero-based optimization process for mains:
Activities | Issues / Constraints |
Basic Parameters | . |
Verify database | Check for currency and complete actuarial sample test (field or desktop) |
Establish design and performance parameters | List performance parameters to be adopted in models consistent with corporate objectives |
Project forward demand | Adopt demand projection in accordance to planning statistics. |
Size Optimization | . |
Establish process | Optimization methodology Calibrated model / data |
Establish representative network(s) | Network(s) typical of other areas if a total network model is not available |
Select network models | Network optimal size |
Specify network layouts | Network connectivity Current customers to be served |
Specify inlet points for each network | Maintain current inlet points if transmission pipelines optimal |
Specify loads applicable to elements of network | Predict demand for gas on a customer basis. Allow defined growth where capacity now available. |
Model pressures/ flows | Adopt appropriate practice consistent with current design philosophy |
Length Optimization | . |
Establish representative network that has been optimized (from above) | Network representative of age profile |
Remove unnecessary interconnections Remove redundant or duplicate mains | Ensures sufficient connectivity/ security of supply |
Re-optimize for size | Account for pressure variation |
Establish optimized model networks in terms of length & size | Apply re-optimization outcomes to all selected model networks Length reductions Size distribution |
The overall optimization process is shown below:
Asset or system optimization in a network is usually quite complex, depending on the elements involved. Optimization based on numbers is straightforward, for example, the number of lift stations required is optimized to match the actual number of customers and the demands of elevation, topography and other such factors. Optimization based on percentage utilization is possible only if the capacity of the particular asset element is available in a continuous function.
Cost and availability are important issues to be considered in an optimization process. In many situations the capacities of the assets come in step functions, for example, the pipe capacity of a collection or distribution main varies in accordance to the size of the pipe available and hence it may not be possible to optimize pipe sizes strictly based on the percentage utilization criteria. Optimization in this case can be achieved only through discrete selection of pipe sizes to match the actual requirements.
System designs, particularly those related to long lead times, are usually completed in steps in anticipation of load forecasts. Typical examples are lift stations, the design for which follows the system augmentation steps, usually with a planning horizon of 5 to 10 years. Optimization of lift stations should therefore be based on the ‘excess capacity’ available through over design, ie ‘the excess augmentation steps’ and not the conceptual actual requirements. This is illustrated in the following diagram.
Industry practice may also affect the extent of optimization. For example, a gas distribution network may theoretically require a 25mm pipe size but a 40mm diameter is the minimum practical main size as the industry standard. Also, the cost differentials between different diameter pipes at the lower size range may be minimal.
Many experts believe that, in reality, optimization should only be completed back to the asset configuration and size necessary to the meet the load predicted in the ‘planning horizon’ necessary for that asset type.
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