Quality conversion
Gas from production fields that is injected into the national gas transmission grid may be different in composition and, consequently, may have a different calorific value as expressed in the Wobbe index. Sometimes gas of a higher calorific value needs to be converted to gas of a lower calorific value. GTS will do this by means of so-called quality conversion. GTS offers quality conversion for shippers as a paid service.
If the average Wobbe index is higher on the entry side of a portfolio than on the exit side, the shipper will need to contract quality conversion. GTS will indicate which Wobbe label is relevant for each entry point or exit point. A Wobbe label is the average Wobbe index for a specific point and is used for the contracting and settlement of the quality conversion instead of the continually fluctuating Wobbe index. There are four standard Wobbe labels: H, L, G+ and G.
Conversion of gas with a lower Wobbe index to gas with a higher Wobbe index, also known as reverse quality conversion, is permitted insofar as GTS can use this operationally. This reverse quality conversion is based on backhaul of the physical quality conversion. GTS will inform shippers if reverse quality conversion should be ended in connection with insufficient physical quality conversion.
Quality conversion can be contracted from GTS as a firm service. Quality conversion can also be contracted as an interruptible service. Interruptible quality conversion can only be contracted after the firm quality conversion capacity is sold out.
Firm quality conversion will be subject to an annual tariff. Interruptible quality conversion will be subject to a rate of 90% of the annual tariff. As with transport services, bookings on a monthly and a daily basis are possible. A monthly factor of 12.5% will apply to monthly bookings. For contracts of 12 months or less, a tariff will apply that equals the sum of the monthly factors multiplied by the annual tariff with a maximum of 100% multiplied by the annual tariff. A tariff of 1/15 times the monthly factor multiplied by the annual tariff will apply for daily bookings.
The amount of the quality conversion used on an hourly basis will be determined afterwards on the basis of allocations. The shipper will have to make an estimate of the required quality conversion volume himself. The quality conversion volume is determined by multiplying the average realised gas flow by the (flow-weighted) average Wobbe label difference between entry and exit points.
Hourly quality conversion volume is calculated retrospectively ar portfolio level, as follows:
- Win = flow-weighted average Wobbe label for entry points
- Qin = total flow at entry points
- Wout = flow-weighted average Wobbe label for exit points
- Qout = total flow at exit points
- Wobbe-delta = maximum { 0; (Win - Wout) }
- Quality conversion = Wobbe-delta x (Qin + Qout) /2
Please see at Online application forms to apply for booking.
