Q & A > Water and Wastewater Management
Date  Replies
18/03/2021 Q: Why is the resin bed height higher in a cation exchanger than in an anion exchanger in a demineralization operation?  
04/02/2021 Q: What is the mechanism for mercury desorption from crude oil pipelines during emergency shutdowns upstream? Does it effect the normal mercury concentration after resuming t operations?  
25/12/2020 Q: How to handle ethanol above ground storage tank drainage? (1)
14/12/2020 Q: Here are a few points regarding the desalter issue in our refinery:
1. There are two desalter trains installed in parallel.
2. When the desalter current fluctuates, the brine water coming out of the desalter has an opaque black colour.
3. The events occur only at one train. In this case, the rest of the trains are fine with the same crude. 4. The events tend to occur at crude switch or introduction of slop oil, but this is uncertain.
What are the possible causes? Please advise what we should investigate and analyze to clarify the causes.
31/10/2020 Q: Is there a practical solution for converting HPS to BFW? for some reason, we can only access HPS while we need BFW for temperature control in the steam reformer. (1)
13/10/2020 Q: We experienced an aromatics leak to the cooling water system one month ago. When we routed the contaminated water to our waste water treatment, it didn’t show any significant change. However, recently we experienced low F/M in our aeration basin. Is it normal to have this delayed response of about 30 days after introducing aromatics contaminated water to the waste water treatment plant? (4)
20/07/2020 Q: Our desalter unit is working fine, the crude oil outlet to the CDU is "clean", there is no water and low metals content. However, there is an issue with the outlet water. When the desalter is "washing" low sulphur content crude oil the water has a huge content of oil in water, grams per liter, and what looks like asphaltenes on the interface. When running high sulphur crude this issue doesn't occur. We did some lab tests; strangely we can not get the same outcome as what happens in the desalter. The water is clean and there are no issues on the water interface. Does anyone know what might be the issue? (1)
05/06/2020 Q: Will the pH of phenol in an aqueous phase (no hydrocarbon) affect how well phenol is decomposed through mixing with air? If it does, is the decomposition more advantageous at a lower or higher pH?  
01/05/2020 Q: I have a problem with my sour stripper column

Feed :
NH3 = 796 ppm
H2S = 324 ppm
pH = 8,7

Product (Sour Water Stripped)
NH3 = 136 ppm vs max 50 ppm
H2S = 5 ppm vs max 10 ppm
pH = 5,8

Why does the pH of sour water stripped (product) decrease significantly with the NH3 content still high? What happens with this process? I have added to the ratio of the reboiler but NH3 still is high. And now, my temperature reboiler sour water stripper cannot increase (indicating fouling). Anyone help me?
12/11/2019 Q: Hello, In our hydrogen production plant we have our own steam generation system that produces 36 bar of steam at 390 degree C temperature. Steam produced in the steam drum has a continuous blow down vessel. We noticed that the conductivity analyzer goes so high that it reaches to NAN sometimes as it automatically reaches to its normal values without any external steps taken by us. We are curious about this automatic adjustment of conductivity in blow down. We have checked the instrument as well, but there is no issue with the analyzer. It is to be noted that the BFW is mixed with condensate separator before pressure swing adsoprtion. The condesate water first goes to degasifier and then mixed with demin water and then pumped to steam drum where steam is made. From couple of days pH of condensate is very low due to low inlet temperature due to dissociation of carbon dioxide, which made pH low. Kindly tell us if there is any reason for high conductivity as per our case. (1)
08/11/2019 Q: We are operating cooling tower with circulation rate of about 10,000 m3/hr. Recently a case of oil ingress occurred through one of the coolers in a process unit. This oil ingress resulted in increasing the cooling water supply temperature from 29 degC to about 36 degC. Although oil content in the cooling tower has been reduced to below 10 ppm by appropriate chemical dosing the problem of high CWS temperature still persists. Cooling tower fans and CW distribution through fills have been checked and found to be working fine. Can anyone suggest some measures for reducing this CW supply temperature back to normal? (2)
08/11/2019 Q: We are operating cooling tower with circulation rate of about 10,000 m3/hr. Recently a case of oil ingress occurred through one of the coolers in a process unit. This oil ingress resulted in increasing the cooling water supply temperature from 29 degC to about 36 degC. Although oil content in the cooling tower has been reduced to below 10 ppm by appropriate chemical dosing the problem of high CWS temperature still persists. Cooling tower fans and CW distribution through fills have been checked and found to be working fine. Any measures for reducing this CW supply temperature back to normal?  
04/10/2019 Q: In our CO2 degassifier, the inlet concentration is 100 ppm when the outlet iş 50 ppm. The system has impregnated wood to seperate CO2(g) from the cationic water. What kind of effect has a high concentration of CO2 on anionic column and boiler feed water?  
17/06/2019 Q: The wash water quality standard from NACE and most articles I have read recommend using phenolic water in either desalters or crude overheads only. I have not found an example of any reuse of stripped sour water from a SWS with phenolic water (FCC or coker sour water) feeds for wash water on a hydrotreater effluent train wash water injections. I have read through articles on polymer fouling in the sour water stripper itself due to phenols and one corrosion book cited kerosene color issues with phenols. Other than that most articles just say phenolic water is recommended for desalter usage mainly but don't call out the specific issues of phenolic stripped sour water for hydrotreater wash water. Are the accompanying cyanides and HSS the main concern, concentrating up at the injection site, or are there concerns with the phenols themselves being injected downstream of the hydrotreater? Are there any examples of diluting phenolic stripped sour water with other streams and reusing it in hydrotreaters if you don't have enough sources of non-phenolic stripped sour water? (2)
18/12/2018 Q: I saw an answer in Q&A, that portable electric desalters will screen the demulsifiers. I would like to screen some of my demulsifiers using portable electric desalter (PED). Can anyone suggest the suppliers of PED? it would be a great help. (3)
13/12/2018 Q: Reprocessing slop oil is always a headache issue for refiners, in our refinery, we blend recovery oil (one of slop oil from crude tank cleaning) into heavy crude slates (API<28), but suffering problem on desalter operation, higher emulsion layer led to electric field trip and desalter brines contain oil which can result wastewater treatment plant in upset, we would like you could share the operating experience on reprocessing slop oil with minimal impact on these facilities, thank you~
(1). What kind of pre-treating methodology did you apply on slop oil before reprocessing? Water separation or any filtration steps?
(2). Did you use chemicals for slop oil pretreatment?
(3). How did you reprocess slop oil? In-line injection into CDU uint or blend slop oil into crude tank?

11/12/2018 Q: In our distillation column we are treating Natural Gas Condensate with 76 ppm sulphur, Acidity < 0.05 mg KOH and organic chloride <0.3 ppm and water content < 0.05%. but designer did not keep any caustic, corrosion inhibitor and Ammonia dosing provision due to combat corrosion at overhead line. Also they did not keep any DM water flushing provision (for fouling control within the tubes of aero condenser). Is it ok not to keep above provision as per above spec of NGC or NGL? But we are draining the overhead drum water separating boot approximately 10-15 litres per day where PH remains 5 to 5.5. So, do we need to use NH3, Caustic and corrosion inhibitor in order to keep PH more than 6? Moreover, do we need to inject DM water at the up stream of Air cooler to eliminate fouling problem as well as increasing PH by the dilution of DM water? (3)
02/12/2018 Q: Why anion resin exhausted before cation resin in ion exchange water treatment? (1)
23/11/2018 Q: Why anion resin is exhausted before anion resin in ion exchange process in water treatment? (1)
27/10/2018 Q: In Our Sour Water Stripper Unit, The quality of Stripped Water is as follows:
H2S :0.4 PPM(Max.10 PPM)
NH3: 2.4 PPM (Max 50 PPM)
Ph: 8.9(6-8)

The H2S and NH3 are in desirable range but still we couldn't get lower Ph in stripped water? Is any other factor causing low Ph?
13/03/2018 Q: We have kerosene hydro bone unit (desulphurization unit) , we faced technical problem which is non-improving (WSIM) water separometer index modified specification .
what is the mean thing that effect in (WSIM), and how can we improve it?
By the way, the reactor system of kerosene hydro bone unit is isolated.
13/12/2017 Q: Why does PH increase in effluent water from electrical desalters? And what is the reason for monitoring such PH levels? (2)
09/12/2017 Q: I am interested in the forum's experience on (full) reusing of processing condensates from conventional Natural Gas / LPG steam reforming Units (from all major licensors). I have experience with an ex-KTI (Technip) based NG SMR whereby process condensates are fully a) fully reused in the BFW system post a simple air stripping for removal of dissolved CO2 and b) steam produced (at 40 barg) is used for both internal needs and export to other process user and a steam turbine / generator. The system operates as such successfully for many years. I understand that recent designs (and at higher steam pressures) call for either a) the steam not to be exported or b) a dual steam raising system one for internal consumption (where the process condensates can be recycled) and another for export steam on clean BFW. This, due to issues with organics difficult to be removed from the BFW and generated in the shift reactors.
Any experiences / views on this ?
13/11/2017 Q: I have question regarding the Reverse Osmosis membranes (RO) and we use anti scale chemical for the RO unit , please could you tell me what will be the effect if we inject the anti scale over rate injection and under rate as well? Is there a specific test to do for this chemical (anti scale ) to find out the optimal performance?  
29/08/2017 Q: Hypothetical: A hydrocarbon contamination is observed in the cooling water system for almost a month. Exchangers and pumps utilizing cooling water (CW) were inspected in the process area however, the cooling water supply is already hazy thus the CW return is also hazy already. The use of biodispersant is being considered to clean up the system. Laboratory testing of the hydrocarbon collected is also being done to determine the contaminant's quality. What more should be done to solve this contamination issue? Will the laboratory result be accurate? The cooling towers are open loop and evaporation of hydrocarbon may take place. (3)
30/03/2017 Q: What are the sources of phenol in overhead condensate (sour water) in a vacuum distillation unit? (2)
16/02/2017 Q: We observed that our crude unit naphtha stabilizer column overhead water has become decolourized since few days. The colour is yellowish to brown. However, the main column overhead water is clear in colour as previously. Can anyone help me in identifying the possible causes for this? Some forming also has been observed while draining this water. Can overdosing of corrosion inhibitor (filming amine type) cause this issue?

Further info:
Thanks for valuable answers. The colour was observed while draining of the vessel boot. So, there is no much time to react with atmospheric oxygen. Is it any dissolved oxygen that react to give the colour? Also, I found some evidence of overdosing (almost double ) of the corrosion inhibitor for a short period of time. Once it was corrected the colour was improved. But, not sure whether it is due to that or due to anything else.
19/01/2017 Q: Can we use utility water as water injection to desalter? What's the Max TDS in the water injection to desalter ? (1)
15/01/2017 Q: What is the best technique in terms of cost and time for online sealing of valve body leakage in which high pressure boiler feed water is streaming?  
12/08/2016 Q: I have a question regarding desalter brine quality, as follows: The desalting of same crude is done by two desalters of different geometry (not two stage desalting, two CDUs). I underline that desalting is done efficiently in both units with respect to salt content in desalted crude. The difference is in the content of sulfides in desalter brine. The desalter that has lower sulfide content in brine is more cylindrical, while the another one "tends to be more spherical". The higher sulphide content represents higher load for waste water treatment plant. My opinion is that this behaviour can occur because of longer residence time of oil and wash water in emulsion volume (or the volume ratio of emulsion volume and total desalter volume). I think that perhaps the emuslifier dossage or or delP on mixing valve are higher. Has anybody faced similar issue in the refinery? Any opinion and experience would be helpful. (2)
11/07/2016 Q: We are facing a problem due to the high content of phenol in LPG treatment spent caustic. Due to this high levels, we are having problems to discard this to the wastewater system.
I do not expect to have such levels of phenol (over than 5000 wppm) in a caustic solution used only to treat LPG. Is it normal to have high phenol content in these type of spent caustic? The sulphides level is lower than this.
The LPG is produced in a Delayed Cooking Unit and is previously treated in a amina section to remove H2S. The caustic treatment is a Merox type, but due to some operational problems, the caustic strengh used is 17%. The phenol level is high even in the spent caustic of the extraction section.
31/05/2016 Q: Our client has recently started processing heavy crude slates from Western Canada. They are having an issue with their Desalter Brine Treatment Unit (BTU, which is a pre-treatment plant for oily solids removal before being sent to the de-oiling train) with higher than design temperatures and light hydrocarbon carry over. Does anyone have experience with this issue? Is steam stripping prior to BTU an option for dealing with this issue?

Thank you for the responses so far. This has provided some insight into the issue. As a follow up, is there any experience with steam stripping of the brine. I believe some refineries in US have this unit for BTEX removal. How efficient would this be for light hydrocarbon removal? Also any insight into requirement of an equalization tank upstream and if solids removal is recommended upstream of the stripper?
28/01/2016 Q: What is the purpose of pre-heating the sour water feed (by exchange with the bottoms of the column) before entering the sour water stripper, if it will increase H2S content and water? (6)
14/12/2015 Q: How much fuel gas (typically) can be used as stripping medium for the treatment of sour water (i.e. 150-170 kg of steam per m3 of sour water)? (2)
10/02/2015 Q: What is the effect of temperature on phenol removal from sour water (sour water from FCCU) in the crude oil desalter? (1)
10/02/2015 Q: Why is caustic added in the SWS column?
22/12/2014 Q: In our RFCC we have a purge treatment unit to remove the catalyst fines from the flue gas before leaving through the stack. The PTU utilizes about 25 m3/hr water for scrubbing and this water after clarification and oxidation leaves the unit as discharge. I would like to know about the possible destinations for the treated PTU water and availability of alternate methods which does not require water for scrubbing. (1)
25/10/2014 Q: For boiler feed water production we use lake water. I am interested to which lab methods are available for determination of humic and fulvic acid in water. Which filters are the best for their removal?

18/06/2014 Q: Do anybody have experience in treating Brine from desalters through Tricanters to separate Oil and sludge from Brine? (2)
01/06/2014 Q: Sour Water stripping = Shell side of feed bottom exchangers containing stripped water is chocking with salts. What could be the reasons? (3)
31/05/2014 Q: We are facing rapid chocking problem of our feed bottom exchangers of sour water feed/stripped water. In last maintenance, tube side of these exchagers (Sour Water) there were found amonium salts deposited in form of lumps, that ultimately traveld through tower and back in the shell of these exchangers. These have cuased serious flow restrictions at stripped water pump due to insufficent suction. To examine this phenomena suction straniner of feed pump were opened but found almost clean. That shows nothing is coming from the feed tank. Please guide upon possible cause of this salt built up in shell and tube type feed bottom exhangers. (4)
27/05/2014 Q: How could I simulate a Boiling Feed Water dearator on PRO II. flash drum? distillation column?  
13/05/2014 Q: Our sour water stripped is fed with Sour water from our hydrocracker unit with respectively 40 000 ppmw and 35 000 ppmw of NH3 and H2S content and a pH of 9. Typical Residual NH3 and H2S in stripped water are respectively in a range of 50 ppmw and 0.5 ppmw. We recently observed that residual NH3 content in stripped water incresaed up to 2000 ppmw while residual H2S remained at low normal value. No change noticed on operating conditions. We also noticed an increase of ammonia content in waste water from vaccum fractionnator overhead vacuum system in the same range (2000 ppmw).
We tried to incresase live steam to feed ratio with no subsequent result.
What could be possible cause and what could we do to solve this problem?
28/04/2014 Q: Who has a reliable cutting water backwash filter for water that has fines and oil residues? (2)
22/03/2014 Q: We want to drain CDU Desalter Effluent Brine to Oily Sewer. Any issues of H2S or smell? (3)
01/02/2013 Q: What is the objective of phosphate injunction in the cooling water network and in any steam disengaging drum in the steam system? (2)
22/12/2012 Q: Which neutralization method is best for batchwise production of acidic effluent? (1)
22/03/2012 Q: I am working in DHT Plant diesel hydrotreater unit and face a proplem with Tempered water system that show the Iron High in Tempered Water System and make Troubleshooting we drain the system many time and make chemical cleaning some time it gone ,but after time it come High
we Drain the system completely to remove any residual contaminants and Isolate the amine sample coolers for one week and cleaning and Add N-2819M to achieve a molybdate.
how do we solve this problem with the Iron and PH.
What is the source of the iron coming ??!!
23/11/2011 Q: What is the safe spill control procedure of the 98% sulphuric acid inside the plant for environment management and safety management?
Maximum quantity stored is 200Lit with dyke, but no secondary disposal means from dyke.
16/09/2011 Q: What is the best way to treat waste water that contains high sulfinol to discharge level? (2)
16/09/2011 Q: I have a question about DeSOx Unit of RFCC
Our plant has a DeSOx unit that removes SOx and spent Cat’ (=dust) in Regenerator flue gas to meet environment standard.
After removing SOx and spent Cat’ by Mg(OH)2 solution, the waste water that includes suspended solid like spent cat’ is removed through filter press.
Filter press is dual type. When one is working, the other is stand-by. (Running time :18~30hr)
Because operation time of the two filter presses is not fixed and unknown, the cleaning man has to stay on or near the filter press to clean it, when switching.
So I want to ask:
1. How do you treat resulting waste water to meet environment regulation?
2. If you use filter press, what is the best way of managing it?
05/09/2011 Q: Can anyone give me a tip off on how to reduce high COD between 200,000-500,000 from sulfenol/amine waste in the gas plant.
04/04/2011 Q: Our overhead wash water which is demineralised water addition is not continuous at CDU plant. Water is added to 2 bundles in 4 hrs. Then water is added to the next 2 bundles and so on. This implies that the 1st bundle in which water is added receives wash water after a gap of about 1.5 days. We use neutralising amine and keep ph between 5.5-6.5 while having almost no corrosion on overhead lines (monel cladded). Caustic is also added at the downstream of the desalter. The contractor who provides services and chemicals is claiming that addition of more wash water to have continuous wash will decrease the consumption of neutralising amine. In our opinion this will not work since the amount of wash water will have no impact on the mass of chlorides available in overhead stream. Would you please comment. (4)
19/02/2011 Q: What are the fundamentals to separate hydrogen sulphide and ammonia from two stage sour water stripping unit? (3)
03/01/2011 Q: Which is to be preferred in a cooling water system: Side Stream Filter or Gravity Filter? (1)
30/10/2010 Q: What are the advantages of using of a 3-phase centrifuge decanter compared to a 2-phase one for oily sludge dewatering? (1)
15/08/2010 Q: we have an induced draft double-flow, cross flow cooling tower...using air to cool condensate water.
the tower fans has two speeds; low & high...In winter, usually low speed is used as the air temperature is low enough (Egypt), so that it reduces the water temperature by an acceptable manner. However; the water is found to exit from where the air enters -the louvers- while, through high speed operations in summer, this doesn't occur.
08/07/2010 Q: We have a very strange problem, it's that the desalter outlet crude has greater salt content than that of the inlet... the lab examinations proved that more than once...this always happens when the injection water is cut off-while switching from a tank to another. What could explain this?

Additional info/response:
1. We cut off water while switching between tanks because of the existing water accompanied with the crude from the new tank; I mean the first 30 minutes after switching to a tank, the crude has too much water to inject more.
2. How could the NaOH type could affect this situation?
06/07/2010 Q: What is the best way of judging the efficiency of a desalter? (6)
04/05/2010 Q: We are hydro-skimming crude refinery with cracking units, from last few months we are having higher Phenolic Compounds Contents in our waste water effluents. Also we do not have any waste water treatment unit in our refinery.
Could anyone tell us main sources of Phenols in waste water of a hydro-skimming refinery? Also why higher phenols are avoided in waste water effluents?