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Month: September 2022

Types of Liquid-Solid Separation

Rifka Aisyah 1 Comment

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

Material Balance for Process Involving Recycle

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Recycle process is process in which a flow stream is returned to an earlier stage in the processing stage. The process is frequently used in the production facility. If the conversion of valuable reactant is considerably less than 100%, the unreacted material is usually separated and recycled. An example of a recycle process in which there is no reaction is the return of the reflux to the top of distillation column.

What do you think about the existence of recycle in material balance calculation?

In my opinion, recycle makes material balance calculation is more difficult. In this post, we will learn material balance for process involving recycle. I hope it will give you a little insight.

Without recycle process, the material balances are simple. The material balance can be carried out in serial, in which the calculated flows out of one unit become the feeds to the next. But if a recycle stream is present, then at the point when the recycle is returned, the flow will not be known as it will depend on downstream flows not yet calculated. Without knowing the recycle flow, the sequence of calculations cannot be continued to the point where recycle flow can be determined. Read More

Difference between Conversion and Yield

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It is important to differentiate between conversion and yield. Sometimes, these terms are mixed up. So, in this post, I want to share the difference between conversion and yield. I also will show you three examples of these terms.

Conversion is to do with reactants (reagents). On the other hand, yield is to do with products.

Conversion

Conversion is a measure of the fraction of the reagent (reactant) that reacts. The conversion of a particular reagent is often less than 100% to optimize reactor design and to minimize formation of by-product.

If more than one reactant is used, the reagent on which the conversion is based must be specified.

Conversion is defined by the following equation: Read More

How to Calculate Percentage of Excess Air in Combustion Process

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In this post, I want to share how to calculate percentage of excess air flow in combustion process. The known data are:

  1. Fuel composition
  2. Flue gas composition

Before we jump into the calculation, we need to understand about excess air and why we need it.

To ensure complete combustion of the fuel used combustion chambers are supplied with excess air. Excess air increases the amount of oxygen to the combustion and the combustion of fuel. When fuel and oxygen from the air are in perfect balance – the combustion is said to be stoichiometric.

The combustion efficiency increases with increased excess air – until the heat loss in the excess air is larger than the heat provided by more efficient combustion.

Let’s see example below. Read More

Material Balances Calculation in Tie Components

Rifka Aisyah

In previous post about material balances, we can see that the flow of any component was in the same ratio to the flow of any other component, as the ratio of the concentrations of the two components. If one component passes unchanged through a process unit it can be used to tie the inlet and outlet compositions.

This method is very helpful for handling combustion calculations if the nitrogen in the combustion air is employed as the tie component and flows through unreacted.

Let’s see example below.

Carbon dioxide is added at a rate of 20 kg/h to an air stream and the air is sampled at a

sufficient distance downstream to ensure complete mixing. If the analysis shows 0.5%v/v CO2. Calculate the air-flow rate. Read More