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Simple Calculation Methods to Estimate Power Required to Rotate Agitator Impeller

Rifka Aisyah

This post is a little different from usual. Honestly, I seldom dealing with agitation process. As you may know from my posts, my projects are mostly in oil and gas field. So, agitation process is very rare in oil and gas processing. However, I think I need to learn something beyond what I already learned until now to improve myself.

In this post, I want to share simple calculation methods to estimate power required to rotate agitator impeller. In the future, maybe I will deal with project involving agitation process. Read More

How To Calculate Required Wall Thickness and Schedule of Pipe

Rifka Aisyah

In this post I want to share how to calculate minimum required wall thickness and schedule of pipe. Before we jump into calculation steps, let’s review what pipe schedule is.

Pipe schedule expresses thickness of pipe. It is not actual measurement, but as a guide based on wall thickness formula.

Two pipes with the same diameter may have different schedules, which means they have a different wall thickness. So, somebody specifying a pipe for a high-pressure application will select a bigger number which represents a bigger schedule or thicker wall.

I made a simple spreadsheet on how to calculate required wall thickness and schedule of pipe. I found that the calculation is quite mechanical. Maybe some process engineers, even me, do not really used to this calculation. The calculation involves allowable stress, weld quality factor, etc. I do not think all process engineers should understand about how to calculate pipe wall thickness. But it would be better if we do.

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How to Estimate Hydrate Inhibitor to Depress Hydrate Formation

Rifka Aisyah

In previous post, I shared what is hydrate formation and primary conditions promoting hydrate formation. Quick review, hydrate in natural gas system is a physical combination of water and other small molecules to produce a solid which has an ice-like appearance. Hydrate should be control because it will cause several problems. The problems include restriction in flowlines, causing physical damage to chokes and instrumentation. One method to control hydrate formation is to inject hydrate inhibitor into production stream.

Read more: Hydrate Prediction using Pressure-Temperature Correlation Read More

Sizing Horizontal Three Phase Separator

Rifka Aisyah

In this post I want to share how to size horizontal three phase separator. The steps used in this post were from Surface Production Operations by Ken Arnold & Maurice Steward. You can learn the details and equations used from the book. In the end of this post, I share free spreadsheet on how to size horizontal three phase separator.

The calculation used in the spreadsheet in for preliminary calculation only. As for fabrication, you may need to discuss more with related vendors and EPC constructors.

Required Data for Horizontal Three Phase Separator Sizing

To size horizontal three phase separator, we need the following data:

  • Oil rate, water rate, and gas rate
  • Operating pressure and operating temperature
  • Properties (density, viscosity) of oil and gas, respectively
  • Retention time of oil and water, respectively
  • Droplet size of liquid and oil to be removed

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Several Types of Three-Phase Separator

Rifka Aisyah

Three-phase separators are pressure vessel that are designed to separate and remove the free water from a mixture of crude oil and water. The term of “three-phase separator” is normally used when there is a large amount of gas to be separated from liquid, therefore the size of the vessel is determined by gas capacity equation.

In addition of three-phase separator, there is term called “free-water knockout”. “Free-water knockout” is generally used when the quantity of gas is relatively small compared to the quantity of oil and water. Therefore, the dimension of vessel is determined by oil-water separation equation. Read More

How to Determine Design Pressure

Rifka Aisyah

As process engineer dealing with process equipment, we need to determine design pressure. For a vessel, design pressure is called maximum allowable working pressure (MAWP). The MAWP determines the setting pressure of relief valve and must be higher than vessel’s operating pressure. Operating pressure is fixed by process condition.

Table below recommends a minimum differential between operating pressure and MAWP so that the difference between operating pressure and relief valve set pressure provides a sufficient cushion. If the operating pressure is too close to the relief valve setting pressure, small surges in operating pressure could cause the relief valve to activate too soon.

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How To Estimate Vessel Weight

Rifka Aisyah

Estimating vessel weight is not usual daily task of a process engineer. However, I found it useful to know how to estimate vessel weight, when we need to estimate vessel cost. In other chance, civil engineer also asks about vessel weight to design the equipment foundation.

To better estimate vessel weight, we need to understand vessel weight components. Those are weight of the shell, the weight of the heads, and the weight of internals, nozzles, pedestals, and skirts. Read More

Sweep or Purge Gas Requirement for Flare

Rifka Aisyah

In many gas plant, flares are always installed to burn waste gases containing combustible components, such as methane, carbon monoxide, and hydrogen. The waste gases are piped to a remote, usually elevated location, and burned in open flame in ambient air using a specially designed burner tip, auxiliary fuel, and in some cases, assist gases like steam or air to promote mixing for nearly complete.

As mentioned in several posts, combustion requires three ingredients: fuel, an oxidizing agent (typically oxygen in air), and heat (or ignition source).

Flare Purge Gas and Flare Sweep Gas

In flare system, a pipe connection for purging or sweeping purpose is usually installed. Flare purge gas means gas introduced between a flare header’s water seal and the flare tip to prevent oxygen infiltration (backflow) into the flare tip. For a flare with no water seal, the function of flare purge gas is performed by flare sweep gas.

Flare sweep gas means the gas intentionally introduced into the flare header system to maintain constant flow of gas through the flare header to prevent oxygen build up in the flare header. Read More

Sizing of Amine System for Natural Gas Sweetening

Rifka Aisyah

In this post I want to share how to size amine system for natural gas sweetening, especially for MEA and DEA. For other amine systems, the licensee should be contacted for detailed design information. In the end of this post, I share simple spreadsheet on how to estimate amine circulation rate, minimum contactor diameter, and reboiler duty of amine system.

Amine absorber

Amine absorbers provide intimate mixing between amine solution and sour gas. Typically, small diameter towers use stainless steel packing, while larger towers use stainless steel trays.

For preliminary design, a tray spacing of 24 in and a minimum diameter of capable of separating 150 to 200 micron droplets can be assumed. The size of packed towers must be obtained from vendor.

Commonly, amine absorbers are equipped with integral gas scrubber section in the bottom of the tower. The function of the scrubber is to remove entrained water and hydrocarbon liquids from the gas, therefore it protects amine solution from contamination.

Separate scrubber vessel can also be provided so that the tower height can be decreased. The vessel should be design using two-phase separators.

For MEA systems with large gas flow rate, a scrubber should be considered for the outlet sweet gas. It is because it will be helpful to reduce MEA losses in the overhead sweet gas. DEA systems do not require scrubber because vapor pressure of DEA is very low. Read More

Sizing Iron Sponge Units for Sulfur Removal in Natural Gas

Rifka Aisyah 1 Comment

In last post we learned about one type of sulfur removal which is using iron sponge unit. Brief review, iron sponge is economically applied for gas containing small concentration of hydrogen sulfide, usually below 300 ppm. Iron sponge unit can not be used to remove carbon dioxide.

In this post, I want to continue the topic about iron sponge unit. More specifically about how to preliminary size iron sponge unit.

At least there are four parameters that we want to know in sizing iron sponge units:

  1. Minimum diameter of iron sponge vessel
  2. Maximum diameter of iron sponge vessel
  3. Required bed height
  4. Quantity of iron sponge
  5. Bed life of iron sponge between change out

Vessel Diameter

Why do we need to know minimum diameter of iron sponge vessel? Read More