Process Description
Water with trace amounts of oil suspended in it is pumped from the Skimp Pit SU-821 to the In-line Chemical Mixer MX-841 where it is adjusted for optimal pH by the injection of Sulfuric Acid solution. Flocculant, a chemical solution that promotes coalescing of the trace oil in the water into larger droplets, is also injected into the feed water to the DAF Unit.
pH-adjusted water flows from MX-841 into the Flocculators R-843A/B which operate in series. The Flocculators provide agitation and residence time to promote the intimate mixing of the flocculant with the feed water. The water flows downward through channels that separate each Flocculator and then through a third channel into the Dissolved Air Flotation Basin T-851.
The flocculated water enters the flotation section of the DAF Basin near the bottom. Circulating clarified water with dissolved air is returned into the DAF Basin through a sparger to distribute the circulating water along the bottom of the basin. At the near-atmospheric pressure of the basin, the dissolved air is released from the clarified water and creates microbubbles throughout the bottom of the DAF Basin.
These bubbles rise as the water flows gently upward because of an inclined baffle in the DAF Basin. These microbubbles help lift the oil droplets that have been formed in the Flocculators. This separation by flocculation, coalescing and flotation results in clarified water that is essentially completely free of oil.
The clarified water flows over the inclined baffle and is drawn to the other side of the DAF Basin by the circulation of DAF Recycle Pumps P-852A/B. The clarified water passes through a set of perforated pipes into another chamber in the basin that supplies clarified water to P-852A/B. The net clarified water then flows up and over another vertical baffle into the clarified basin. Because the DAF Basin is elevated above the ground on a support structure, clarified water flows by gravity to the DAF Surge Tank T-861.
DAF Compressor C-851 is a small, rotary-type air compressor that injects a small flow of compressed ambient air into the clarified water from DAF Recycle Pumps P-852A/B. The DAF Air Saturator Tank V-851 has a packed bed that promotes the dissolving of air in the circulating water. V-851 operates at a high pressure which promotes the dissolving of the air, too. Clarified water from DAF Surge Tank T-861 is pumped to discharge facilities at battery limits by Water Discharge Pumps P-861A/B.
Coalesced oil that floats on the top of the water in the DAF Basin spills over a weir into the oil collection chamber. A set of rubber wiper blades on a rotating belt (not shown on Schematic #35) gently push the oil on the surface toward the oil collection chamber. Collected float oil then flows by gravity to the DAF Float Tank T-871. Float Transfer Pumps P-871A/B transfer the float oil the Recovered Oil Sump SU-831 in the Oily Water section.
Water with trace amounts of oil suspended in it is pumped from the Skimp Pit SU-821 to the In-line Chemical Mixer MX-841 where it is adjusted for optimal pH by the injection of Sulfuric Acid solution. Flocculant, a chemical solution that promotes coalescing of the trace oil in the water into larger droplets, is also injected into the feed water to the DAF Unit.
pH-adjusted water flows from MX-841 into the Flocculators R-843A/B which operate in series. The Flocculators provide agitation and residence time to promote the intimate mixing of the flocculant with the feed water. The water flows downward through channels that separate each Flocculator and then through a third channel into the Dissolved Air Flotation Basin T-851.
In-line Chemical Mixer MX-841 is a special mixing device that is engineered to promote intimate mixing of injected chemicals with feed water from Skim Pit Pumps P-821A/B. Prior to entering the Flocculator compartments of the Dissolved Air Flotation basin, sulfuric acid from Sulfuric Acid Pump P-841 is injected into the feed water to decrease its pH from 7.90 to 6.52. This represents the optimum pH of the water to maximize the coalescence efficiency of the flocculant to produce coalesced oil in the DAF Basin. A flocculant is a chemical that promotes coalescence of the suspended solids into larger particles so they can be more easily separated from the water. The flocculant is injected into the feed water by Flocculant Pump P-842. The flow rates of the sulfuric acid and the flocculant are very small compared to the feed water flow rate.
Sulfuric Acid Pump P-841 is a chemicals injection pump outfitted with a variable frequency drive (VFD) on its electric motor to control its speed and, therefore, the injection flow rate of sulfuric acid. The pump is supplied from the Sulfuric Acid Drum D-841 at battery limits. The design flowrate of sulfuric acid is 1.3 GPH.
Flocculant Pump P-842 is a chemicals injection pump outfitted with a variable frequency drive (VFD) on its electric motor to control its speed and, therefore, the injection flow rate of flocculant. The pump is supplied from the Flocculant Drum D-842 at battery limits. The design flowrate of flocculant is 0.1 GPH.
The Flocculators R-843A/B are chambers within the DAF Basin T-851. Feed water from In-line Chemical Mixer MX-841 flows down along and under the feed baffle of Flocculator R-8431A. Agitator AG-843A circulates the water and flocculatant mixture within the chamber of R-843A to ensure intimate contacting of the flocculant and the suspended solids. This mixture then passes into the chamber of Flocculator R-843B in the same way. This chamber is agitated by AG-843B. The flocculated water from R-8431B then flows over its exit baffle and down into the Dissolved Air Flotation Basin’s (T-851) main chamber.
The flocculated water enters the flotation section of the DAF Basin T-851 near the bottom. Circulating clarified water with dissolved air is returned into the DAF Basin through control valve PCV-859 and then into a sparger to distribute the circulating water along the bottom of the basin.
At the near-atmospheric pressure of the basin, the dissolved air in the water from the DAF Air Saturator Tank V-851 is released from the clarified water and creates microbubbles throughout the bottom of the DAF Basin. These bubbles rise as the water flows gently upward because of an inclined baffle in the DAF Basin. These microbubbles help lift the oil droplets that have been formed in the Flocculators. This separation by flocculation, coalescing and flotation results in clarified water that is essentially completely free of oil.
The clarified water flows over the inclined baffle and then passes through a set of perforated pipes into another chamber in the basin that supplies clarified water to P-852A/B. The net clarified water then flows up and over another vertical baffle into the clarified water basin. Because the DAF Basin is elevated above the ground on a support structure, clarified water flows by gravity to the DAF Surge Tank T-861.
The DAF Recycle Pumps P-852A/B are electric motor-driven centrifugal pumps that recirculate clarified water from the DAF Basin through control valve FV-857 to the DAF Air Saturator Tank V-851. The flowrate of the recycled water is normally 100 GPM.
DAF Compressor C-851 is a small, rotary-type air compressor that injects a small flow of compressed ambient air through control valve FV-858 into the top of DAF Air Saturator Tank V-851. The compressor is driven by an electric motor. The design flow rate of compressed air is 160 SCF/H. The injected air flow is relatively small because only enough air to assist in gently lifting oil to the surface is needed.
The clarified water from DAF Recycle Pumps P-852A/B flows into the top of DAF Air Saturator Tank V-851 and downward across a packed bed within V-851. Compressed air from C-851 is sparged into the water above the packed bed to evenly distribute the air in the water. The air dissolves in the water at high pressure in V-851. The air-saturated water leaves the bottom of V-851 and flows back to the DAF Basin through self-regulating control valve PCV-859, which maintains high pressure in V-851.
Water flows by gravity from the clarified water basin of T-851 through isolation valve XV-861 into the DAF Surge Tank T-861. T-861 is a fixed-roof tank and can hold about 1.5 hours of design discharge water flow.
Clarified water from DAF Surge Tank T-861 is pumped by Water Discharge Pumps P-861A/B through control valve FV-861 to discharge facilities at battery limits. These pumps are electric motor-driven centrifugal pumps. The normal flow rate of the water discharge flow is 144.7 GPM. In case of low level in T-861, the pumps will be protected against damage from running dry.
Skimmed float oil from the oil collection trough of DAF Basin T-851 flows by gravity through isolation valve XV-871 into the DAF Float Tank, T-871. T-871 is a smaller fixed-roof tank that holds about 2 hours of float oil.
Float Transfer Pumps P-871A/B are small electric motor-driven centrifugal pumps that transfer the float oil from T-871 to the Recovered Oil Sump SU-831 in the Oily Water section. Normally, one of the pumps is set up to automatically drain T-871 periodically. The pumps can also be operated manually.
Fuel gas is normally supplied directly from 1ST Stage Discharge Separator D-311 through isolation valve XV-901 to Fuel gas KO Drum D-901. D-901 operates at approximately the same pressure as D-311 (45.5 PSIG). In case gas is not available from D-311, domestic fuel gas is supplied from battery limits through control valve PV-901 and isolation valve XV-901 to D-901. Note that domestic fuel gas is natural gas (mainly methane) while gas form D-311 is a mixture of methane, ethane, propane and butane.
D-901 separates out and collects any condensate that may be present in the gas from D-311 or from the domestic fuel gas supply. Collected condensate is disposed in the Closed Drain Drum D-941 through control valve HV-901 as needed. Normally there is no significant accumulation of condensate in D-901.
Fuel gas flows to various units in the Oil Terminal from the top of D-901. These include:
- Degasser D-111 (intermittent, for pressure control as needed)
- Slop Tank T-121 (intermittent, for pressure control as needed)
- HP Flare System Pilot X-955 (continuous)
- HP Flare Header (continuous, for purging)
- LP Flare System Pilot X-965 (continuous)
- LP Flare Header (continuous, for purging)
- Hot Oil Heater F-922 (continuous)
- Hot Oil Heater F-924 ( on stand-by)
- Hot Oil Surge Drum D-921 (intermittent, for pressure control as needed)
Instrumentation
MX-841
AI-840 indicates the turbidity of the water from the Skim Pit Pumps PU-821A/B.
AI-841 indicates the pH of the water feed to the In-line Chemical Mixer MX-841.
AI-843 indicates the pH of the water leaving MX-841.
P-841
Hand switch HS-841 is used to start/stop the motor of Sulfuric Acid Pump P-841. On a trip of I-841, HS-841 is locked in the STOP position to avoid injection of acid without sufficient water flowing through MX-841 which can cause damage to the mixer and downstream piping.
FIC-841 controls the flow rate of sulfuric acid to MX-841 by adjusting the speed of P-841. On a trip of I-841, FIC-841 is locked in manual mode with an output of 0%.
P-842
Hand switch HS-842 is used to start/stop the motor of Flocculant Pump P-842. On a trip of I-841, HS-841 is locked in the STOP position to avoid injection of flocculant without sufficient water flowing through MX-841 which would be wasteful.
FIC-842 controls the flow rate of flocculant to MX-841 by adjusting the speed of P-842. On a trip of I-841, FIC-842 is locked in manual mode with an output of 0%.
R-843A/B
LI-843A indicates the level of water in the chamber of Flocculator R-843A.
Hand switch AG-843A is used to start/stop the motor of the agitator for R-843A.
LI-843B indicates the level of water in the chamber of Flocculator R-843B.
Hand switch AG-843B is used to start/stop the motor of the agitator for R-843B.
T-851
Hand switch HS-854 is used to start/stop the motor of the Scraper of the DAF Basin T-851.
LI-854 indicates the level of water in the main chamber of T-851. LI-851 indicates the level of clarified water in the collection well at the end of the DAF Basin assembly.
AI-856 indicates the turbidity of the clarified water flowing from the collection well to T-861.
P-852A/B
Hand switches MOV-852A/B open and close the suction MOVs (motor operated valves) on P-852A/B, respectively.
Hand switches HS-852A/B are used to start/stop the motors of DAF Recycle Pumps P-852A/B.
FIC-857 controls the flow of DAF recycle water by adjusting the position of control valve FV-857.
C-851
Hand switch HS-856 is used to start/stop the motor of DAF Air Compressor C-851.
FIC-858 controls the flow of air to the DAF Air Saturator Tank by adjusting the position of control valve FV-858.
T-861
Hand switch XV-861 opens and closes inlet isolation valve XV-861.
LI-861 indicates the level of clarified water in T-861.
LAHL-861 independently indicates the level of water in T-861. It is used by interlock I-861 to stop the Water Discharge Pumps P-861A/B on low water level.
PU-861A/B
Hand switches MOV-861A/B open and close the suction MOVs (motor operated valves) on P-861A/B, respectively.
Hand switches HS-861A/B start and stop the motors of P-861A/B, respectively. Normally only pump “A” is in operation. These switches are locked in the STOP position on activation of interlock I-861 to prevent operation on low level which could lead to pump damage.
FIC-861 controls the flow of water from P-861A/B to discharge facilities at battery limits to by adjusting the position of control valve FV-861.
T-871
Hand switch XV-871 opens and closes inlet isolation valve XV-871.
LAHL-871 indicates the level of float oil in T-871. This indication is used by control interlock I-871 to automatically start and stop the motors of either of the Float Transfer Pumps P-871A/B on high and low level.
P-871A/B
Hand switch HS-875A is used to determine if one of P-871A/B is to be operated automatically or manually. Normally, HS-875A is in the AUTO position.
Hand switch HS-875B is used to select which pump “A” or “B” is to be automatically controlled by control interlock I-871. Normally, HS-875B is in the “A” position to automatically control P-871A. Normally, P-871A automatically runs every 40 minutes for about 10 minutes.
Hand switches MOV-871A/B open and close the suction MOVs (motor operated valves) on P-871A/B, respectively.
Hand switches HS-871A/B are used to manually start/stop the motors of P-871A/B. These switches can be adjusted at any time, even when a pump is set to be automatically controlled.