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How To Do Projects Economic Evaluation

Rifka Aisyah Leave a comment

In this post, I want to share how to do projects economic evaluation. In my experience, doing project economic evaluation is not always daily activities of process engineers. However, when I involved in feasibility study project, we need to do projects economic evaluation. Also in my own experiences, as process engineers focused on creating several alternatives of process configuration, our team from industrial engineers did the projects economic evaluation. However, it will not hurt to understand general idea of project economic evaluations 😊

Since investing in chemical plants is done to make money, a system for evaluating project economic is required. For small projects, the decision-making process can typically be simplified by comparing the capital and operating expenses of various processing methods and pieces of equipment. When choosing between large, complicated projects, especially when the projects differ significantly in scope, time frame, and product type, more advanced evaluation procedures and economic factors are required. In this part, some of the more popular methods of economic analysis and the standards by which economic performance is evaluated are described. Read More

Preliminary Sizing of Cyclones

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In this post, I want to share how to do preliminary sizing of cyclones.

Cyclone is the most common and effective gas-solids separator that uses centrifugal force. They can be constructed from a variety of materials, are generally simple structures, and can be designed to operate at high temperatures and pressures.

The reverse-flow cyclone is the most common design. In a reverse-flow cyclone, the gas enters the top chamber tangentially, spirals down to the conical section’s apex, and then moves up in a second spiral with a lower diameter before leaving through a central vertical pipe at the top. The solids travel radially to the walls, down the walls, and then are gathered at the bottom. Read More

Preliminary Sizing of Hydrocyclones

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In this post, I want to share how to do preliminary sizing of hydrocyclones. In previous post, hydrocyclones are utilized for solid-liquid separations. The centrifugal force is produced by the motion of the liquid in this centrifugal device, which has a stationary wall. Like a gas cyclone, the gas cyclone operates on much the same principles. Hydrocyclones are inexpensive, reliable separators that work with particle sizes ranging from 4 to 500 micron. Figure below shows hydrocyclones typical proportion geometry.

Hydrocyclone typical proportion
Hydrocyclone typical proportion

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Basic Sizing Equation for Sedimentation Centrifuges

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In this post, I want to share basic sizing equation for sedimentation centrifuges. Based on previous post, sedimentation centrifuges used to separate materials based on the density difference between the solid and liquid phases. They are usually used to produce cleared liquid.

Basic sizing equation for sedimentation centrifuges use the term sigma (Σ). The sigma is used to describe a performance of a centrifuge regardless of the physical characteristics of solid-fluid system. The sigma value is equivalent to the cross-sectional area of a gravity settling tank with the same clearing capacity. The sigma value is often expressed in cm2.

The sigma theory is a description of how centrifuge performance is described. It offers a way to compare sedimentation centrifuge performance and to scale up from laboratory and pilot scale experiments. Read More

Types of Liquid-Solid Separation

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Most process industries require the separation of solid and liquid phases, and several techniques are utilized to accomplish this. Figure below shows several types of liquid-solid separation techniques.

Liquid-solid separation methods
Liquid-solid separation methods

Gravity or centrifugal force can be used to separate materials based on their different densities, or in the case of filtration, the particle size and shape. The best method to apply will be specified by the solids concentration, feed rate, size, composition of the solid particles, the objective of separation (clear liquid or solid product), and degree of dryness of the solid required. Read More

How to Estimate Thermal Conductivity of Liquid

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Thermal conductivity of a material is a measure of its ability to a particular material conduct heat. In the international system of units (SI), thermal conductivity is measured in watts per meter-kelvin (W/(m.K)). In imperial units, thermal conductivity is measured in BTU/(h·ft·oF).

Thermal Conductivity of Solids

Solid composition, shape, structure all affect how well it conduct heat. Many handbooks provide thermal conductivity of solids for frequently used engineering materials.

Thermal Conductivity of Liquid

Equation below can be used to estimate thermal conductivity of liquid.

Estimate thermal conductivity of liquid
Estimate thermal conductivity of liquid

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How to Estimate Density of Liquid Mixture

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In this post, I want to share how to estimate density of liquid mixture. This calculation is very simple yet useful for process engineers.

Density of liquid mixture can be estimated from density of pure components in the mixture. Many handbooks have a large database of density of pure liquids. Density of most organic liquids usually lies between 800 and 1000 kg/m3, except than those containing a halogen or other “heavy atom”.

Density at normal boiling point can be obtained from the molar volume. Read More

Material Balances involving Unsteady-State Process

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In previous posts, I shared how to calculate material balances of several cases. Those calculation involve steady-state condition. In steady-state process, the accumulation is zero. The streams flowrate and composition are also did not vary with time. The calculation are more complex if these conditions are not met. The unsteady-state behaviour of a process is important when considering the process start-up and shut-down, and the response to process upsets.

Unsteady-state material balances are solved by setting up balances over a small increment of time, which results in a set of differential equations that describe the process. These equations can be solved analytically for simple problems. Computer-based methods would be employed for more difficult problems.

Example below is an example of general approach used to solve un-steady state problem. Read More

Material Balances Calculation Involving Purge Process

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Bleeding off a portion of the recycle stream is important in a production process to avoid the accumulation of undesirable material. For instance, if inert components from a reactor feed are not separated from the recycling stream in the separation units, they would build up in the recycle stream until they made up the whole stream. To keep the inert level within reasonable level, some of the stream would need to be purged. Normally, a continuous purge would be employed. Assuming steady-state circumstances:

Loss of inert in the purge = Rate of feed of inerts into the system

The concentration of any component in the purge stream will be the same as that in the recycle stream at the point where the purge is taken off. Consequently, the relationship shown below can be used to calculate the necessary purge rate:

[Feed stream flowrate] × [Feed stream inert concentration] =

[Purge stream flowrate] × [Specified (desired) recycle inert concentration]

Let’s see example below. Read More