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How to Determine Cake Resistance in Filtration Systems

Rifka Aisyah 2 Comments

Purpose of this post is to determine cake resistance in filtration systems, as a function of operating pressure of filter. Before we jump into the calculation, let us learn first several basic calculation in filtration system.

As filtration proceeds, a porous cake of solid particles is built up on a porous medium, usually a supported cloth. The flow of liquid is laminar because of the fineness of the pores. Therefore, the following equation represented the phenomena:

Q = \frac{{dV}}{{dt}} = \frac{{A\Delta P}}{{\mu R}}

The resistance R is made up of filter cloth Rf and that of cake Rc which may be assumed proportional to the weight of the cake. Read More

Introduction to Filtration

Rifka Aisyah 2 Comments

These days, I feel like learning topics related to solid processing. After I learned about agitation process and its scale-up, I want to learn about filtration process.

So, in this post I want to share you general preview of filtration process. Honestly in my career until now, I already handled one project related to filtration equipment, which is my very first project: pre-feasibility study of carboxymethyl cellulose plant. The filtration equipment used in the project was rotary vacuum filter.

I hope by learning and writing what I read here in this blog will refresh my knowledge and hopefully useful in the future projects. Read More

Step-by-Step Methods on Nongeometric Scale-up for Liquid Agitation

Rifka Aisyah

This post would be quite long since agitation scale-up involved trials and evaluation of the parameters. This post is based on Handbook of Chemical Engineering Calculations Fourth Edition by Nicholas P. Chopey.

To understand better about how to scale-up nongeometric liquid agitator, I will use an example. We will make one change at a time to understand its effect.

The example is below:

A process involving water-like liquid must be scaled up from an agitated 18-in diameter, 15-gallon pilot-scale reactor to a 120-in diameter, 7000-gal large scale reactor.

The pilot scale has a 18-in straight side and the large-scale reactor will have a 168-in straight side. Both reactors have ASME dished heads on the top and bottom.

Successful process performance was obtained in the pilot scale with two 6.0-in diameter pitched-blade turbines operating at 350 rpm. It is proposed that the large-scale reactor use hydrofoil impellers instead of pitched-blade turbines, for improved liquid motion.

Each pitched-blade turbine has a turbulent power number of 1.37 and each hydrofoil has a power number of 0.3.

Past scale-up experiences with similar processes, but with geometrically similar tanks, were successful when impeller tip speed was held constant. Read More

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