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Month: October 2021

Classification of Capital Cost Estimation

Rifka Aisyah

Based on my experience, in almost every stage of project, capital cost estimation is always part of document deliverable. During feasibility study, Pre-FEED study, or during FEED (Front-End Engineering Design), capital cost estimation is always created. But there are several degrees of capital cost accuracy between those studies. In this post I want to share classification of capital cost estimation.

I believe that capital cost estimation is more art than science. The more experience a cost estimator gets from cost estimation, the more accurate the estimation. In many cases, an estimator must use considerable judgment in preparing the estimates.

Classification of Capital Cost Estimation

There are at five types of fixed cost capital estimates:

  1. Order-of-magnitude (ratio estimate). It is rule-of-thumb methods based on cost data from similar-type plants are used. The probable accuracy is -30% to +50%
  2. Study estimate (factored estimate). This type requires data such as preliminary material and energy balances and major equipment items. The probable accuracy of -25% to +30%
  3. Preliminary estimate (budget authorization estimate). This type needs more details about the process and equipment, such as design of major plant items are required. The probable accuracy is -20% to +25%
  4. Definitive estimate (project control estimate). The data needed for this type of estimate are more detailed than preliminary estimate and include preparation of specification and drawings. The probable accuracy is -10% to +15%
  5. Detailed estimate (firm estimate). To prepare this type of estimate, complete specification, drawings, and site surveys for the plant construction are required. The probable accuracy is -5% to +10%

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Gas Sweetening using Iron Sponge Process

Rifka Aisyah 1 Comment

Iron sponge process is economically applied for gases containing small concentration of hydrogen sulfide (H2S), usually less than 300 ppm, operating from low to moderate pressure in a range of 3.45-34.5 barg (50-500 psig). Iron sponge process cannot be used to remove carbon dioxide.

Iron sponge process is the oldest and still the most widely used batch process for sweetening of natural gas and natural gas liquids. Overall, iron sponge process has the following characteristics which make it still attractive to be applied: simple process, low capital cost, and relatively low chemical (iron oxide) cost. Furthermore, pressure has a relatively little effect on its adsorptive capacity of a gas sweetening agent. Read More

Firefighting Foam Demand Calculations

Rifka Aisyah

Firefighting Foam has been widely used as a fire extinguisher for flammable and combustible liquids for many years. It is consisted of premix solution (a ratio of water and foam concentrate) mixed with air. It forms a stable form blanket which spreads above the fuels and adheres to surfaces.

Foam forms a film above the fuel surface and seals vapor. Fire fighting foam concentrate prevents fuel contact with oxygen, resulting in fire suppression. It also has a high cooling effect and will avoid reignition. Read More

Inert Gas Consumption for Tank Blanketing Calculator

Rifka Aisyah

In this post I want to share calculator to estimate inert gas consumption for tank blanketing. Please be noted that the result is average inert gas consumption. For peak consumption, please check my previous post.

I think this is the second time I created calculator. I am quite satisfied with the results because I used plugins.

I hope you find this post useful.

Inert Gas Consumption for Tank Blanketing

Rifka Aisyah 1 Comment

Inert gas is used to blanket certain fixed-roof tanks for safety. Nitrogen is a common inert gas used for the purpose. In addition to safety of storage tank, the benefit of tank blanketing includes improved product quality and equipment life cycle.

Why nitrogen is commonly used in tank blanketing?

Nitrogen has inert properties, wide availability, and relatively low cost at any economic efficiency. Other gases, such as carbon dioxide or argon, are also sometimes used for certain application.

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Condensate RVP (Reid Vapor Pressure)

Rifka Aisyah

In 2014, I have involved in multi-billion dollars EPC project in Indonesia. The project handled gas and condensate. For condensate, it was stated that the quality shall meet certain RVP (Reid Vapor Pressure) value. In this post, I want to share what RVP is.

Definition of RVP (Reid Vapor Pressure)

Stabilized condensate generally has a vapor pressure specification. Its specification is usually identified by its Reid Vapor Pressure (RVP) or True Vapor Pressure (TVP).

Reid Vapor Pressure (RVP) is related to the vapor pressure of a petroleum product, which measures its inherent tendency to evaporate at 100oF with vapor:liquid ratio of 4:1 (ASTM D323). RVP is a function of hydrocarbon’s composition and is independent of operating temperature and pressure. The value of RVP lies below the true vapor pressure.

The higher the RVP, the more quickly the condensate or  oil will vaporize into the air. Read More