Skip to main content

Design of Air-Cooled Exchanger (Part 2)

This post is continuation of air-cooled exchanger design (part 1). In this post, I want to share free spreadsheet of air-cooled exchanger design. I used sizing procedures from GPSA engineering data book.

Please differentiate between heat load and motor power. I sometimes found young engineers confused heat load with motor power, especially when listing equipment load list.

I found many resources in internet about how to size air-cooled exchanger. We can size air-cooled exchanger easily by inputting necessary variables. For example, I used Checalc to calculate air-cooled exchanger. But, it is necessary to understand what we do.

The hardest part of sizing air-cooled exchanger by using spreadsheet is so many data to check in charts/graphs. For example, friction factor, physical property factor, and correction factor. I hope we can be patient to handle this.

Please check my spreadsheet about how to size air-cooled exchanger. I hope you find this post useful.

Air Cooled Exchanger

Design of Air-Cooled Exchanger (Part 1)

Air-cooled exchangers are used to cool fluids with ambient air. They should be considered when cooling water is in limited or expensive. Air-cooled exchangers are used for cooling and condensing.

Principle of air-cooled exchanger
Principle of air-cooled exchanger [1]
Air-cooled exchangers consist of banks of finned tubes over which air is blown or drawn by fans mounted below or above the tubes. Air-cooled exchangers are classified as forced draft when the tube section is located on the discharge side of the fan, and as induced draft when the tube section is located on the suction side of the fan. Read More

Recommended Safety Distance for Siting and Layout of Facilities

Facility layout is one of many document deliverables in a project. Do you know the philosophy to create facility layout? In this post, I want to share a siting and layout approach, as well as recommended safety distance for siting and layout of facilities by Center for Chemical Process Safety (CCPS) of the American Institute of Chemical Engineers (AIChe).

The siting philosophy begin with a review of the material and processing hazards, such as toxicity, flammability, explosivity, reactivity, or a combination of these hazards. Other potential hazards should also be considered since they may be unacceptable to their surrounding community, such as odors, loud noises, or the light from flares.

Once the type of hazards have been identified, their potential off-site and on-site impacts can be addressed. This step includes how the local terrains affects the release scenarios. At the same time, the layout of the process units and associated areas within the facility, such as storage tank areas or flares, should be arranged to reduce risks. The layout of the equipment, including both orientation and distance between them, may affect day-to-day operations. Therefore, it is important to address the balance between reduced or increased distances and the impact on accessibility when evaluating the on-site consequences. Read More

Gas Dehydration Design with Glycol Solutions

Natural gas contains many contaminants, one of them is water. When the gas is transmitted to the surface from processing and finally pipeline transmission, its pressure and temperature reduced naturally in the well string. This reduce the capacity of natural gas to hold water vapor and free water is condensed. The water vapor must be reduced to meet sales gas requirement, which is usually around 2-7 lb/MMscf.

For many years, glycol solutions have been used for natural gas drying. Early glycol dehydration units utilized diethylene glycol (DEG). Triethylene glycol (TEG) came into use around 1950 primarily because its higher boiling point thus gives better separation of water and greater dew point depression without causing thermal decomposition of the glycol. Tetraethylene glycol (T4EG) has been used in some specialized cases, but in majority, triethylene glycol is used.

In this post, I want to share preliminary design of gas dehydration unit using glycol solutions. Calculation and formulae used in this post can be accessed through this link. Read More

Conversion Higher Heating Value (HHV) to Lower Heating Value (LHV)

As a process engineer dealing with gas project, I usually involve in these terms, higher heating value (HHV) and lower heating value (LHV). Do you know the differences between these two?

In simple words, higher heating value (HHV) includes energy used to vaporize water. While lower heating value (LHV) excludes energy used to vaporize water.

Which water?

Water contained in the original energy form or created during the combustion process.

If we put them into equation, then it will be like this.

Relationship between HHV and LHV
Relationship between HHV and LHV

Read More

Estimation of Gas Turbine Fuel Rates

In this post I want to share how to estimate gas turbine fuel rates. We use heat rates to estimate gas turbine fuel rates.

Heat rate is a measure of thermal efficiency or the amount of energy (in the form of fuel) which must be input to the gas turbine to produce the output power. Heat rate is usually expressed in terms of Btu/(hp.hr) or Btu/(kW.hr) based on the lower heating value of the fuel. Heat rate and thermal efficiency are related as follows:

Gas turbine heat rates vary considerably. They are function of gas turbine rating and type of turbines, which are simple cycle, jet turbine simple cycle, or regenerative. Read More

How To Estimate Capital Cost of Pipeline Project

In this post I want to share how to estimate capital cost of pipeline project. For your information, this procedure is for information and general guidance only. Source of this procedure is from Gas Pipeline Hydraulics by E. Shashi Menon. The book was published in 2005. So, the cost might need adjustment due to inflation.

Before we jump into estimation, we need to understand scope of pipeline project to easily define component of cost. There are ten (10) major cost components of pipeline project:

  1. Pipeline
  2. Compressor stations
  3. Mainline valve stations
  4. Meter stations
  5. Pressure regulating stations
  6. SCADA and telecommunication
  7. Environmental and permitting
  8. Right of way acquisitions
  9. Engineering and construction management
  10. Allowance for funds used during construction and contingency

Read More

Reciprocating Compressor Power Calculation Part 3 (Four-Stage Compression)

In previous post, I shared how to calculate reciprocating compressor power if number of compression stage is two and three, respectively. In this post, I will use the same problem/example to estimate reciprocating compressor power if number of compression stage is 4. In the end of this posting series, I will show you the difference of each stage and to see how important to determine number of compression stages.

The method used to calculate reciprocating compressor is the same, whether it is two-stage, three-stage, or four-stage. There are several steps which is repetitive.

Example

Compress 2 MMscfd of gas measured at 14.65 psia and 60oF. Intake pressure is 100 psia, and intake temperature is 100oF. Discharge pressure is 900 psia. The gas has a specific gravity of 0.80 (23 MW). What is the required horse power?

Assuming number of stages is 4 Read More