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Quantitative Risk Analysis Techniques Part 1

Last time I involved in quantitative risk analysis (QRA) project in LNG regasification facility as supporting process engineer. Actually, I did not involve in QRA project itself, but I involved in back pressure study. In order to get to know about this field, I want to share you some basics quantitative risk analysis techniques as mentioned in several literatures, such as BS EN standards and AiChE publications.

Quantitative Risk Analysis is a procedure to accommodate management with event scenarios, measure of likelihood, and magnitute of potential losses. After risk analysis, we want to manage the risk by several means.

  • Reduce the frequency of accidents
  • Reduce the consequence of accidents
  • Provide insurance 

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How to Calculate NSPH of Pump with Examples and Illustrations

NPSH of pump (net positive suction head) should be calculated/predicted in the beginning of pump sizing. The purpose is to check if the pump will work appropriately. Liquid pressure will lower right in inlet of pump impeller. If pressure reduction is lower than vapor pressure, liquid phase will change to vapor phase. The impeller rapidly collapses vapor bubbles which cause cavitation and damage.

In this post I will share you how to calculate NPSH available, which is net positive suction head calculated based on system arrangement. The value of NPSH available (NPSHA) shall be greater than NPSH required (NPSHR), which is a function of pump and to be specified by pump manufacturer.

NSPH of pump is calculated as follow:

NPSH available (ft, m) = absolute pressure (ft, m)vapor pressure (ft, m) –  line loss (ft, m) ± elevation difference (ft, m) Read More

Cooling Tower Makeup Water Calculation with Example

It’s been a while since the last time I write an article about utility system. In this post I want to share you how to calculate cooling tower makeup water.

Cooling tower must be made up because the water level decrease by the time during operation. There are aspect that contribute to calculation of cooling tower makeup water. Those are:

  • Evaporation loss
  • Drift loss
  • Blow down

Total cooling water makeup water requirement = evaporation loss + drift loss + blow down.

Let’s take a look one by one how to calculate each component.

Evaporation Loss

Evaporation loss is loss of water due to evaporation. It is calculated by this equation:

Evaporation loss = 0.00085 Wc (T1-T2)

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Natural Gas Line Sizing using General Pressure Drop Equation

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

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

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. Read More

Get to Know Toothpaste Composition and What The Function Is

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

Marketing aspect of feasibility study

How to Write Marketing Aspect of Feasibility Study

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