Improving Heat Exchanger Monitoring | RefinerLink
Cor
Cor

RL Blogs

image
Improving Heat Exchanger Monitoring

By Steve Pagani

Sep 01, 2015
 

Heat exchanger monitoring is critical to reducing operating costs and maximizing refinery yields.

 
 

Heat Exchange, just like Distillation, is the bread and butter of refinery process engineering. Heat exchanger monitoring should be one of the top Process Monitoring properties of everyone at the refinery.

 

Why is heat exchanger monitoring so important? Heat exchange is the refinery’s recycling program, so for those yuppie hipster engineers out there this should get you all excited! (just kidding around)

 

When crude oil is shipped into the refinery it’s normally around 60F, but then it must be heated up to several hundred degrees. This initial heat input isn’t free - it cost money in the form of natural gas fired furnaces. Over the course of a year that is worth tens to hundreds of million dollars.

 

Heat exchanger monitoring allows us to measure the efficiency of heat transfer over time. One trick I wish someone would have told me earlier in my career was that heat exchanger monitoring is more about precision that accuracy.

 

In school we get all jazzed up calculating exact heat transfer coefficients. But in reality in a refinery, it’s not quite that simple. Most of the refinery process streams aren’t simple single component streams, so their physical properties already start off as assumptions. At best case refinery heat exchanger monitoring is an estimation to start, so don’t sweat the small stuff focus on the big stuff- temperature and flow rates.

 

Heat exchanger monitoring’s primary purpose is to understand heat transfer as a function of time, so precision is more important than accuracy. Another way of thinking about it is that heat exchanger monitoring is measuring the heat transfer efficiency over time. The heat exchanger efficiency changes over time usually as a function of fouling.

 

Heat exchanger fouling is important to understand because it reduces the heat transfer efficiency causing increased costs to the refinery in the form of extra fuel-energy, pumping-energy (due to reduced hydraulic efficiency), and downtime costs.

 

 

 

 

Heat exchanger monitoring can help process engineers understand the heat exchanger fouling. Macro or micro materials laying down on heat exchanger components cause fouling. Macro fouling can be imagined as obstructions such as pieces of cooling water towers or organic debris getting into cooling water systems.

 

Micro fouling, distinctions are made between:

 

  • Scaling from crystallization of solid salts
  • Particulate fouling
  • Corrosion fouling from corrosion deposits
  • Chemical reaction fouling
  • Solidification fouling
  • Biofouling

 

 

Heat exchanger monitoring is understanding the heat transfer coefficient over time. Critical to these equations is understanding as many heat transfer parameters as possible.

 

Ideal information for precise heat exchanger monitoring:

 

  1. Cold fluid inlet and outlet temperature
  2. Hot fluid inlet and outlet temperature
  3. Hot fluid and cold fluid mass flow rate (not just volume!)
  4. Pressure change hot and cold fluid across the heat exchanger

 

 

In the past engineers were limited to the temperature readings operators made once a shift during their daily rounds. Over time the refining industry added electronic temperature indicators allowing continuous tracking of temperatures through IT systems. However, during this initial phase the cost of data was expensive, and to the disbelief of process engineers everywhere not all the data was measured in the IT systems.

 

Now the cost of data is miniscule compared to the benefits of energy refinery efficiency. With the introduction of hand held systems, wireless monitors, and infrared tools, process engineers can close all the holes preventing precise routing heat exchanger monitoring.

 

Heat exchanger monitoring tips:

 

  1. Understand the data available through temperature, flow, and pressure indicators.
  2. Find out what temperatures, pressures, and flows are taken by the operators on their routine duties. If that data isn’t going into an IT system work with your refinery to get this data into some sort of IT system. A stack of old daily plant reading papers in the corner of a control room are worth no more than a roll of toilet paper. If the data is already going into an IT system make sure you have access to them in the heat exchanger monitoring package.
  3. Pressure doesn't lie! Differential pressure (DP) tracking on the tube and shell side of the heat exchanger can offer valuable information.  If DP builds up over time is a sure sign that flow is being restricted by something.
  4. Utilize a hand held temperature gun to close any temperature data information. Hand held infrared temperature guns cost less than a video game. I truly believe that before you hand each process engineer that company phone and laptop they should be given a holster, belt, and an infrared temperature gun.
  5. Know the mass flow rate and pressure drop on both sides of the heat exchanger. This can be a little trickier if your other data systems don’t have this information. Be creative and use wireless technology to help close this gap.
  6. NORMALIZE the data! Here is where the value of that chemical engineering degree should start coming in handy. Do something to help yourself understand if the change in heat transfer efficiency is due to change in the process or because of true fouling. Remember somewhere along the way you’ll recommend to have a fouled heat exchanger opened and cleaned during a turnaround. Nothing is worse that being wrong on those cleaning recommendations.
  7. Use an infrared camera to understand temperature gradients inside the heat exchanger. Obviously this is impossible if the exchanger is thoroughly insulated. But if it is possible, the time and effort required to take an infrared picture once a quarter is well worth the valuable information provided.

 

Heat exchanger monitoring doesn’t have to be rocket science. Just use as much technology as possible to track as much heat transfer data as possible. Simple calculations can allow you to improve heat exchanger monitoring and save your refinery millions of dollars a year.

 
Enjoy this content? Join our Free Newsletter    
  • Ruben Gil Aguirre :   In the following link you can find an application on how to estimate operating heat exchanger fouling factors. It provides a methodology that can be used in the refineries. http://dc.engconfintl.org/cgi/viewcontent.cgi?article=1058&context=heatexchanger2007

    Sep 07, 2015

  • Peter D'Lima :   I'm very intrested in knowing if Sonic Refrigeration, included within the distillation apparatus, could improve the process?

    Sep 07, 2015

  • Mike Newman :   Can you elaborate Tip 6? How do you normalize the data?

    Nov 15, 2015

  • Steve Pagani :   In simplest form, normalize on mass flow rate. There are probably more elaborate statistical methods, but start with just a base line variable (DT/fouling factor/U factor) at a baseline mass flow rate.

    Nov 18, 2015

  • Virnia Patzi :   Really useful.

    Jan 24, 2016

  • Tamer kandeel :   Dear Sirs, Kindly, we need your best price of DEPOSIT MONITORS of cooling tower to continuously monitor for scale prior to any scale forming on heat transfer surfaces Tamer Kandeel Sr. technical support Eng.

    Jun 19, 2016

Do NOT follow this link or you will be banned from the site!

Blog Topics

 

People You May Know