KROHNE ALTOSONIC V EN - Manual (Page 101)

ALTOSONIC V
Operating Manual rev02 E 7.30850.34.00 Page 101 of 106
10.5 Simulated Frequency on failure
If the meter is installed downstream of a separator that can lead to total meter failure due to air/liquid
mix the following function is made to avoid Platform shutdown on meter failure due to gas/liquid
mixture.
Technic & Specification
BC00-32-173:
1.0 Effects of water in oil on USM measurements
1.1 Concern has been raised surrounding the effects of varying levels of water in crude oil that may be
presented to the liquid ultrasonic flow meters that are proposed for fiscal custody transfer on BP Miller
Platform. Levels of water below 5% are considered to be within the USM manufacturer’s level of
uncertainty. The commingled flow of oil and water is homogeneously mixed by the LP pumps and
normal water content does not exceed 1%. At a certain level of water in oil above 5% (yet to be
confirmed) the USM will attenuate or scatter the ultrasonic signals. The overall effect of this will result
in all five paths of the ultra sonic flow meter being lost and no actual flow measurement being recorded
through the metering station. The frequency and duration of these events are historically 1 hour every
two weeks and the levels of water in the crude may vary between 5% and 40%.
1.2
These produced water plant upsets introduce a period of instability when significant quantities of
produced water can be exported to the pipeline although steps are taken immediately by operations to
limit the amount of water being exported. The ultrasonic flow meter will continue to provide accurate
information even after four of the acoustic paths have attenuated. Only after the fifth acoustic path
attenuates will the meter cease to measure.
1.3
When the ultrasonic meter stops measuring it is proposed to provide information from the USM, the
flow computer and the density analyser that will allow a mismeasurement calculation to be carried out.
The Krohne flow computer will generate virtual flow pulses that reflect the last actual flow rate
measured. This information will be time stamped and recorded in a separate trend analysis file
together with the density trends. Once the USM re-establishes an actual flow rate these virtual flow
pulses will stop and the file time stamped. It will then be possible to estimate the amount of oil exported
during these upset periods using a mismeasurement calculation.
1.4
In order to limit the discontinuity during the transient periods of loss of measurement the following
proposals are suggested:
a. On loss of all five probe signals the Krohne flow computer will produce virtual flow pulses to the
SGC flow computer and will not indicate loss of signal for a period of I minute.
b. If, during the I minute period, the flow signals are re-established then real flow pulses will be re-
instated and the SGC flow computer will NOT record a m ismeasu reme nt.
c. If, after I minute, the flow signals are NOT re-instated then the SGC flow computer will start to
record a mismeasurement.
d. The end of the mismeasurement period will be flagged by the Krohne flow computer after real
pulses have been re-instated for at least 10 seconds.
CLNT0300.DAT excerpt:
16 [SIMULATED FREQUENCY (PULSE TRAIN) OUTPUT FOR FLOW]
Upon Velocity Of Sound (VOS) failure on all channels, the UFP will transmit
simulated pulses (flow) on the first frequency output of the MP103 card.
Note that the MP103 should be configured to output the Gross Flow or the
Standard Flow (Section 5) for this feature to work properly.
For a full technical specification of this feature see the AMEC document:
BC00-32-173-issue-0002
16.01 SimulatedFrequency N =#1
//[0..1] 0=OFF, 1=ON
16.02 SimFreqTimer1 =#60 //time before alarm [1..300 s]
16.03 SimFreqTimer2 =#30 //data validation timer [15..150 s]
16.04 SimFreqLowVOS =#1.0 //VOS low limit [1.0..5000.0 m/s]
16.05 SimFreqHighVOS =#5000.0 //VOS high limit [1.0..5000.0 m/s]
16.06 TotalisersUpdate =#0 //[0..1] 0=OFF,1=ON update totals on fail
16.07 SimFlowOnPath =#0 //[0..1] 0=OFF,1=ON SimFlow on path fail