Subject: This paper evaluates the types of Automatic Sampling Devices and their relation to ACT and Commingling of Crude Oil oproduction application.
Background: There have been varying results in Automatic Sampling on ACT and Commingling operations which are directly related to the application of the Sampling device.
The primary difference in a sampling unit used for an ACT installation and one used on a Commingling installation may be stated simply as the difference in accuracy requirements. The rules and regulations set up by the regulatory bodies are not as strict for Commingling as those for ACT installations, therefore, the precision designed sampler is used for ACT and a more simplified form for Commingling.
The principle of Automatic Sampling is common to both applications and basically the same components are used to construct the complete Sampler Unit. Where there is a difference in the sampling device for each application, it will be noted in the discussion. If a specific reference is not made, it is to be understood that the point of discussion is suitable for either an ACT or Commingling installation.
Description of Equipment:
There are two types of Automatic Sampling Devices and they are as follows:
Type I - The Time-Cycle or Non-Proportional Type.
Type II - The Flow Responsive or Proportional type.
Either type may be applied to both ACT and Commingling installations, but with the increased use of the positive displacement meter Type II - The Flow Responsive or Proportional Type is the most commonly used.
We will discuss briefly the Type I - Time Cycle or Non-Proportional sampler, in order that the difference between the two types may be more clearly indicated. First, though, let us look at the definition of the word "Automatic" and the word "Sampling".
By definition, the word "Automatic" means self-acting, especially of mechanical devices. The definition of the word "Sampling" is a small part of anything selected as a sample for inspection or analysis. Therefore, by combining the two definitions, we have a selfacting, mechanical device selecting a small part of anything for inspection or analysis. The actuation of the mechanical device may be accomplished by pneumatic, electric or hydraulic transmission.
The Type I sampler may be a continuous sampler where one or more equal increments of sample per minute is taken at a uniform rate, or an intermittent sampler where less than one equal increment per minute is taken. The continuous or intermittent sampler may be paced or actuated by an electric time clock, either a pneumatic or hydraulic transmitter, if the pulse is transmitted on a definite time interval. The most commonly used transmitter is the electric time clock when electric power is available. This type of sampler is most applicable where custody transfer is made by manual means, such as hand gauging a tank, but Automatic Sampling is desired.
The Time Cycle or Non-Proportional type of sampler is recommended only where the rate of flow is reasonably constant during the entire sampling period.