Closed Sampling

To address these issues, Air BP introduced the concept of ‘closed sampling’ in the early 1980's. The objective was to be able to visually examine jet fuel in a satisfactory manner to ensure the integrity of quality control measures whilst also minimising:

• The amount of product downgraded during sampling processes

• Time spent on the task

• Risk of small spillages

• Operator exposure to product.

Closed sampling is now widely used in aviation fuel depots and on hydrant dispenser vehicles, so that the practice of taking samples in open buckets and glass jars is completely eliminated for all normal operations. Also the quantity of product downgraded to slops is greatly reduced and its

collection centralised.

The basis of this method is a piping circuit incorporating a 'sampling station' and intermediate product collection and recovery tanks through which samples of product taken from filters, tanks or vehicles can be examined, water and dirt removed and clean product eventually returned into storage.

The volume combined in water draw-off lines plays an important part in the efficiency of routine sampling for water from vertical tanks. A sample return tank of typically at least 200 litres capacity should be provided to enable contents of the draw-off line to be captured and to allow fast flushing without danger of splashing or spillage. Examples of product recovery tanks can be supplied by Air BP Centre Engineering. A tanks closed sampling loop is shown in Figure 5-37.

AEG Issue 1 5-68  Air BP 2001 MAIN PRODUCT

RECOVERY TANK

RETURN PUMP FILTER/WATER SEPARATOR

WASTE OIL/

WATER TANK

TANK'S CLOSED SAMPLING STATION TANK

WATER DRAW-OFF LINE PRODUCT RETURNED TO TANK

FIGURE 5-37TYPICAL TANK CLOSED SAMPLING / PRODUCT RETURN SYSTEM

All sampling points should preferably be connected to an approved closed sampling system but manual sampling points are still necessary for

secondary checks or back-up. Manual sampling points shall permit the unhindered drawing of a sample into an approved sampling bucket or glass jar which requires a clear space of approximately 350 mm (14 inches) below the sampling line outlet, see Figure 5-38.

FROM PIPEWORK

350MM

SAMPLING POINT

CAP

FIGURE 5-38PROVISION OF ADEQUATE SPACE BELOW A MANUAL SAMPLING POINT

AEG Issue 1 5-69  Air BP 2001

At depots where there is a frequent need to remove large quantities of water from storage tanks (e.g. following discharges by coastal tankers), it is recommended that a larger (20-50m³) capacity product recovery tank (PRT) is installed. The PRT should be internally lined, sloped to a sump and fitted with a high level alarm. Using suitable piping and valved manifold(s) the PRT should be able to collect product from each of the main tanks and, after settling and testing, clean product should returned (through filtration) to the main tanks.

Fig ?? depot block diagram shows a typical depot incorporating such a sampling circuit. Product is flushed from the sumps of the reception filters, bridger offloading, storage tanks and into-hydrant / fueller loading filters into adjacent 'sampling stations' (1, 2, 3, 4, & 5) where the product can be examined by an operator.

Each sampling station consists of a small 'side tank', a special glass closed sample jar or 'sampler' and interconnecting piping and valves. All of the sampling stations are used in a similar way.

To illustrate how they are used, consider the sampling station (1), adjacent to the storage tank, as shown in detail in Figure 5-39

VENT FROM

FIGURE 5-39CLOSED SAMPLING STATION ADJACENT TO STORAGE TANK

Samples of product are flushed from the tank centre sump through a stainless steel line via a spring-loaded ball valve and a glass tee to a side tank.

The glass tee is used for two reasons. Firstly, the operator can observe the clarity or otherwise of the product as it flows into the side tank and thus immediately has an indication of the condition of the sample. Secondly, when the product in the side tank has settled, the operator can see whether water or dirt is present and can base his future actions on this observation without actually having to take a sample from the bottom of the side tank.

AEG Issue 1 5-70  Air BP 2001

In this case the side tank is a completely closed vessel, with a line to the top of the main tank to prevent an overflow. A sight glass is incorporated in the vent line to let the operator know when the side tank is full.

Similarly, the associated sampler is a sealed unit vented to the top of the main tank.

The capacity of the side tank is chosen so that when it is full the contents of the drain line and the tank sump will have been completely flushed into the side tank. This is to ensure that the sampling process will be carried out on a truly representative sample of product from the tank sump.

After sampling, product drains by gravity from the sealed side tank into a semi-buried product collection tank.

Figure 5-40 shows a typical product collection tank. It is fully automatic in operation - product flows in, a high level switch starts an associated transfer pump and a low level switch stops it again. It cannot overflow as the tank is sealed and vented into the top of the main storage. Suction is from the outlet of a steep conically shaped bottom so water or dirt should not accumulate.

STAINLESS STEEL HANDLES

INLET PIPE

OUTLET PIPE

STAINLESS STEEL TANK BODY

FIGURE 5-40A TYPICAL 100-200 LITRE PRODUCT COLLECTION TANK

In larger depots, more than one product collection tank may be required and these really are just a means of collecting the samples from several side tanks in an immediate area and passing the product on to a central product recovery tank - no sampling is carried out at the collection tanks themselves.

Product from the collection tanks is pumped into an above ground central recovery tank, as shown in Figure 5-41. When the product recovery tank is full it is allowed to settle and then the content of the sump is flushed into an adjacent sampling station.

AEG Issue 1 5-71  Air BP 2001

After confirming that the quality of the product in the recovery tank is satisfactory, the fuel is pumped back through filtration into storage. All water and dirt extracted from the product recovery tank at the sampling station is dropped under gravity into a buried waste oil tank. Periodically a waste oil contractor using a suction tanker takes the contents of the waste oil tank off-site.

TO STORAGE

FROM PRODUCT COLLECTION TANK ABOVE GROUND

PRODUCT RECOVERY TANK

SAMPLER SAMPLE

TANK

PUMP

SUCTION TANKER CONNECTION

BURIED WASTE OIL TANK (DOUBLE SKINNED) GLASS

TEE

MOTORISED VALVE

HIGH LEVEL SWITCH HIGH LEVEL ALARM

HIGH HIGH LEVEL ALARM

FIGURE 5-41TYPICAL LARGE FUEL DEPOT PRODUCT RECOVERY PROCESS

The principal virtues of this arrangement is that it is quick and easy to use, there is no manual sampling or exposure to product at all, there is no waiting around for the side tank to settle and no need for local pumps to return the sampled product back into the main tank.

Figure 5-42 shows the sampling station (4) for the into-hydrant filter/water separators but the same principle is also used for the upstream filters at pipeline reception (3).

AEG Issue 1 5-72  Air BP 2001 DRAIN

HOSE

FILTER WATER SEPARATOR

FILTER WATER SEPARATOR

FILTER WATER SEPARATOR

SAMPLE

TANK SAMPLING

STATION

GLASS TEE TO COLLECTION

TANK

SAMPLER STAINLESS

STEEL TUBING

FIGURE 5-42INTO-HYDRANT FILTERS CLOSED SAMPLING SYSTEM

The sump of each filter/water separator is piped to the sampling station using small bore stainless steel tubing and the valving arrangement allows a sample from each sump to be drawn in turn into the sampler. The tubing diameter and length are chosen to ensure that the contents of the sampler give a true representation of the condition in the sump. The glass tee enables this operation to be monitored as the fuel flowing into the side tank can be inspected visually. Filter/water separators need to be drained for maintenance – this may be done using the closed sampling system.

At the conclusion of the sampling operation the contents of the sample tank are dumped by gravity into a semi buried collection tank and hence pumped automatically to the above ground product recovery tank for separation/recovery.

Overfill protection in this instance is by spring loaded ball valves only, as typically the location of such filter vessels is too far from the main storage tanks to justify completely closing the system.

Figure 5-43 shows a typical bridger offloading sampling arrangement (5).

This allows product to be flushed from the base of the bridger through the offloading hoses into the sample tank and then sample the actual incoming fuel. As before, a glass tee allows both observation of the flow stream plus an assessment, after a few moments settling, of the quality of the fuel in the tank.

AEG Issue 1 5-73  Air BP 2001 TO COLLECTION

TANK

GLASS TEE SAMPLE TANK

SAMPLER BRIDGER

OFF

LOADING TO STORAGE

FIGURE 5-43TYPICAL BRIDGER OFFLOADING SAMPLING ARRANGEMENT

Again the content of the side tank is dumped by gravity to a semi-buried collection tank and hence pumped to the product recovery tank.

Details of typical closed sampling equipment, side and product recovery tanks are given in MECH 90 it doesn’t exist any more.