CNG Filling Stations - That Meet Your Specific Requirements

Planning & decision criteria

Filling mode: slow fill or fast fill

Slow Fill

When designing a CNG fuel station first the question of a suitable filling mode must be clarified.

If the opportunity exists of filling all vehicles of fleet over a longer period of time one can consider the purchase of a Slow-Fill system. Generally this is suitable for smaller vehicle fleets (5-7 vehicles), which can be filled at an in-house depot fuel station in the available schedule intervals or large petrol stations for refuelling bus fleets with more than 20 coaches.

During Slow-Fill tanking the compressor pumps the compressed natural gas directly into the vehicle tank without intermediate storage.

By means of a filling coupling attached to the compressor station the vehicle can now be filled with the delivery quantity of the compressor station in a corresponding period.

Fast Fill

If however the natural gas is intended to be sold to third parties or a large number of vehicles is intended a Fast-Fill fuel station should be selected.

Here the compressed gas is first stored in a triple storage rack, before it is filled into the vehicle tank by flowing through the natural gas filling post. Generally filling times of 1 to 2 minutes (80l cylinders) are attained.

In this instance however the maximum available gas quantity in the triple storage rack must be taken into consideration when filling vehicles as described under storage systems.

Daily Gas Requirements

To select the suitable compressor size first and foremost the number of the vehicles to be filled daily is of great importance.

When designing the system care must be taken that the compressor already should have a daily minimum running time of approx. 8-12 hours as both due to a technical as well as an economic point of view long stand stills should be avoided.

In a design of up to 12 hours compressor running time per day correspondingly an increase in capacity of 50% can be attained without additional components having to be installed, although there is already a good exploitation of the compressor system right from the start.

If due to a strong increase in fuelling demand the gas quantity required can not be supplied the capacity and always be increased by thanks to the modular extendibility of the BAUER systems.

In this instance depending on whether a compressor and or a high pressure storage tank have to be added, an additional module can be added simultaneously whereby the delivery quantity or the gas quantity which can be doubled from the high pressure tank for peak load refuelling.

Irrespective of whether a compressor and storage unit is selected from the MFS, CFS or CTA series with regard to the expanding CNG market the modular extendibility is always an economical solution for a system which is always optimally exploited.

Pre-Pressure in the Gas Line

Another important aspect is the use of pre-pressures in the gas networks.

Through the direct, non-adapted utilisation of the pre-pressure actually present the specific power drain of the compressor and thus the operating costs of the compressor system are reduced as less energy is needed to compress the natural gas which has already been pre-compressed.

When working with pre-pressure however the expected daily running time of the compressor should be decisive as when using booster systems higher deliveries of the compressor generally result due to the higher gas input.
If on using a booster a daily running time of only a few hours results a pre-pressure reduction is also appropriate due to service of capital reasons.

Also an adaptation of the gas input pressure to the maximum permissible compressor input pressure can be useful in so far as high connection costs to a high pressure supply network is to be expected with a lower gas delivery potential. An approximate reference value to be considered is a direct, unadjusted pre-pressure utilisation at gas quantities to be provided daily for vehicle refuelling of approx. 1000 m³ and more.

Depot or Public Refuelling

An additional aspect to be clarified is the type of refuelling with regard to the group of customers.

In the case of a depot refuelling mainly vehicles belonging to the company are refuelled whereby a limited supply is also possible to third parties. In these types of cases a simple dispenser with automatic tank data recording can be selected as these stations are usually operated without any service personnel.

If the refuelling system is to be integrated in a public access gas station such as ARAL, ESSO etc. a filling post must be used which is also available from BAUER and can be connected with the common interface protocols of the different cash till systems.