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Natural Gas Line Sizing using General Pressure Drop Equation

Rifka Aisyah 9 Comments

Line sizing is a part of every engineering activity. Although it is not major part, line sizing is required when we prepare piping and instrumentation diagram. In this post, I want to share you how to do natural gas line sizing (actually the method is applicable for all kind of gases).

I usually use process simulator when it came to natural gas line sizing. Long time ago, I tried to size manually. But the result is not the same as from simulator. But, I tried again and yesterday I got a satisfied results.

Natural gas line sizing calculated in this post will be from manual calculation and from process simulator. API RP 14E is used as reference.

Based on API RP 14E, single-phase gas lines should be sized so that the resulting end pressure is high enough to satisfy the requirements of the next piece of equipment. So, the point is the end pressure. The velocity is also a noise problem if it exceeds 60 ft/s. However the velocity of 60 ft/s should not be interpreted as an absolute criteria. Higher velocities are acceptable when pipe routing, valve choice and placement are done to minimize or isolate noise.

API RP 14E mentioned several approach to calculate pressure drop, but in this post I will use general pressure drop equation. 

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Centrifugal Compressor Power Calculation

Rifka Aisyah 21 Comments

In this post I want to share you how to calculate centrifugal compressor power since there are so many process engineers are looking for it (and I also don’t know how).

To calculate centrifugal compressor power, we need these gas properties: compressibility factor (Z), molecular weight (MW), inlet gas temperature, inlet gas pressure, outlet gas pressure, adiabatic component (Cp/Cv), and mass flow rate.

Let’s start with an example while I show you step-by-step of the calculation method. In this example, we have these gas properties (I use US units).

Compressibility factor (Z) = 0.9972

Molecular weight (MW) = 18.15

Gas constant (R) = 1544/molecular weight

Inlet temperature (T1)  = 546 deg R

Inlet pressure (P1) = 15 psia (don’t forget to use absolute pressure)

Outlet pressure (P2) = 60 psia

K (Cp/Cv) = 1,274

Flow (W) = 0,184 lb/min

The required data to calculate centrifugal compressor power is head. We can use either adiabatic head or polytropic head as long as we use adiabatic efficiency and polytropic efficiency in companion. Read More

Inert Gas Purging Requirement Calculation

Rifka Aisyah 19 Comments

Purging is an activity used to remove oxygen in piping or vessels to certain concentration, for example 2%-mole. It uses inert gas, usually nitrogen, to do that.

In this post, I want to share you how to calculate inert gas for purging activity. There are three different calculation methods used.

Dilution Purging

In dilution purging method, the inert gas simply flows through the vessel and reduces the concentration of unwanted component. It is used for tanks, reactors, and other vessels. Figure below is used to determine requirement of inert gas.

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Get to Know Toothpaste Composition and What The Function Is

Rifka Aisyah Leave a comment

Today I bought a toothpaste from GlaxoSmithKline and got interested in its composition. I actually gained interest in reading composition of various things, but never answered what their functions. In this post I want to share you what I googled about the function of every component in toothpaste. Each toothpaste may have different toothpaste composition. I used this toothpaste brand for example. Please note, this post is not meant to encourage you to buy the product :D. Read More

How to Write Marketing Aspect of Feasibility Study

Rifka Aisyah Leave a comment

In previous post, I wrote about how to write technical aspect of feasibility study. In this post, I want to share you how to write marketing aspect of feasibility study. This topic is important to ensure that the proposed product has market/specific market and to determine how much the capacity of product to be produced.

When I involved in the project, which was reactivation of carboxymethyl cellulose (CMC) plant, I learnt that Indonesia mostly imported CMC from China. Local producers of CMC in Indonesia were only two, PT Humpuss Karboksimetil Selulosa (PT HKS) and the other one (I forgot). The fact that Indonesia imported CMC means there are demand that cannot be met be local supply. So, marketing aspect aspect of feasibility will be started from supply and demand. Read More

Technical Aspect of Feasibility Study based on My Actual Experience

Rifka Aisyah Leave a comment

There are at least two aspects that make a feasibility study sounds: technical aspect and financial aspect. In this post I want to share you the first one: how to make technical aspect of feasibility study.

I have involved in three feasibility study projects. Each project has different technical aspect that being focused. I want to be more practical in this post, so I will share you example of what to write for technical aspect of feasibility study based on my current project.  Read More

Pipe Wall Thickness Chart

Rifka Aisyah Leave a comment

Pipe wall thickness chart is a must-have item for me as process engineer. I usually use it when I have to size pipe, do hydraulic analysis, etc. Information I need from the chart are mostly outside diameter and inside diameter of particular pipe size.

In this post I want to share you pipe wall thickness chart based on ASME B36.19M-2004 Stainless Steel Pipe.

In this chart you can extract data of

  • Outside diameter and wall thickness in inch and mm
  • Pipe size is expressed in NPS (Nominal Pipe Schedule) and DN (Diametre Nominal)
  • Weight in pound per linear foot or kilogram per meter

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PSV

Safety Valve vs Relief Valve (Differences based on API 521)

Rifka Aisyah 2 Comments

Sometimes terms can be confusing. Terms safety valve and relief valve are confusing too. So, to make it clear, let see the definition based on API 521.

Pressure relief valve is a generic term applied to relief valves, safety valves, and safety relief valves. It is designed to automatically reclose and prevent the flow of fluid.

Relief valve is a spring-loaded pressure relief valve actuated by the static pressure upstream of the valve. The valve opens normally in proportion to the pressure increase over the opening pressure. A relief valve is used primarily with incompressible fluids.

Safety relief valve is a spring-loaded pressure relief valve that may be used as either a safety or relief valve, depending on the application.

Safety valve is a spring-loaded pressure relief valve actuated by the static pressure upstream of the valve and characterized by rapid opening or pop action. A safety valve is normally used for compressible fluid.

Can you spot the differences?

Relief valve is used for liquid and open in proportion to the pressure increase, while safety valve is used for gas and open rapidly.

Reference:

API 521 Pressure relieving and depressuring system