Oil Water Separators (API)

The Application

The API Separator is normally the first wastewater treatment step in most petroleum refineries. The API separator is typically the technology of choice for refineries as the primary oil/solids separation step.

The operation of an API separator is based on the difference in the specific gravity of the oils/solids and the wastewater. The majority of suspended solids will settle in the unit. Once the oil and suspended solids are removed from the wastewater, the middle phase water is then sent on for further treatment.

The Problem

The API system takes the waste streams from the entire refinery which can easily push it beyond it’s capacity to separate the oil and water entering the system. During operational upsets from petroleum processes such as de-salters, sour water strippers or process sumps the volume of water causes the API to allow more solids and oil to get through because there is not enough retention time for the solids to drop out of suspension inside the API.

There are 2 common issues that affect the control of an API system:

  • The amount of manual samples needed to insure proper operation of the API (i.e. lack of automation). During a process upset the manual sample interval is not frequent enough to catch the increased organic loading going through the API.
  • Existing online analysis is not adequate to handle the extreme conditions (i.e. sticky oil and high solids) sometimes seen inside a typical API system. Traditional analytical technologies become a maintenance nightmare due to plugging of the sample system.

If enough oil makes it through the API then the down-stream treatment steps may be overloaded and depending on the placement of the API it could cause severe stress on the waste treatment plant or create a potential permit violation if the oil makes it to the sewer or local water source.

There are VOC measurements to also consider when looking at API systems. As the waste water passes through system it has the potential to vent Volatile Organic Carbons. In many cases the refinery will completely enclose the API with a vapor recovery system and burn the VOC’s in a flare. In other cases the API is open and the refinery wants to monitor VOC’s for air permit reasons and to control odor.

The Solution

By continuously monitoring the organic load entering the API system the customer can make decisions to divert the waste water back to the sour-water stripper to try and remove the heaviest solids and then return it again to the API. This option is not always convenient because the sour water stripper is continuously used by many process units and may not have the capacity to handle diverted water from the API, so knowing when they can divert is very important.

By measuring the effluent of the API the customer can quickly recognize if there is a problem with the separator or there is a major process upset which is exceeding the API capacity. This will allow them to respond very quickly to correct the problem before they kill the bacteria in their waste water plant or violate their water permit.

The BioTector can offer quick response to process upsets when other online analyzers can not. With the ability to go from 0-100,000ppm without dilution and the fact that we can operate in many applications without any filtering means that the operational uptime of the analyzer will be in excess of 99.7%.

If there are application conditions that require special sample handling we can offer sample methods that address both chemical compatibility (Sample By Pass Option) and heavy solids (Venturi Vacuum Sampler) which will allow us to provide a better than 99.7% uptime.

The BioTector can also be provided with an on-line VOC option which can provide a TVOC (Total VOC) measurement and still allow the analyzer to make the TOC measurement at the same time without the need for multiple analyzers or having to take the analyzer offline to switch analysis.