We are processing a heavy crude of API 18. Salt content of the crude is 80-100ptb. BS&W is 0.8 to 1.2%.
We are using stripped sour water as wash water, made up by BFW. pH of wash water is between 7-7.5.
We are maintaining a desalter temperature of 150 deg C.
We are having two desalters in series, which is supposed to bring down the salt by 99%. but we reached up to 90% earlier.
Last two months we are having a high emulsion band. The BS&W of desalted crude is 2-3 and the oil in brine is 1-2% even at minimum delta P (0.3kg/cm2). Water injection rate is 3% to individual desalters (circulation not done as oil carryover with brine observed.
The voltage across the grid is as low as 6-10 KV (Tapping at 22KV). We have changed the secondary tapping to 18V and the deslater is showing an improvement in Voltage (10-12 KV)
1.what can be the reasons for this upset?
2. Can you explain the effect of change in secondary voltage?
We are not adding any scavenger to the crude.
Stripped water pH is 6-6.5 and brine water pH is in 7.5 range.
What parameters of crude oil should I check?