Hi everyone. This is Doug Simmers talking again about improving your combustion processes.  The primary goal of combustion flue gas analysis is optimizing the fuel/air ratio, which minimizes fuel cost, lowers NOx emissions, and also minimizes the amount of carbon dioxide greenhouse gases emitted into the atmosphere. One overlooked use of flue gas analyzers is for balancing the combustion across large multi-burner furnaces.

Historically, a single flue gas analyzer placed downstream or in the smokestack was considered satisfactory for setting fuel/air ratios. Many furnace operators have moved the measurement location upstream, closer to the furnace, in order to get a faster speed of response, and added more analyzers for redundancy. This has proven to be a mixed blessing, since the analyzers almost never read the same O₂ levels, which lowers the operators’ confidence in the measurement, and subsequently their willingness to operate at the lowest possible O₂ setpoint. After many calibrations, it becomes clear that all the analyzers are all reading correctly, and the problem is that the combustion inside the furnace is unbalanced. When you think about it, this makes sense.

Four O₂ analyzers placed zone by zone at the top of the radiant section of a process heater furnace.

The combustion process is the burner. This is where the fuel and air are mixed and combusted. The furnace is mostly just a heat exchange envelope. If you have 50 burners in a large furnace, you have 50 discrete combustion processes, and some variability can be expected. This is the case for all large multi-burner furnaces, be they a 500 MW coal-fired boiler, a large crude process heater furnace in a refinery, or a steel reheat furnace.   Strategically placing an array of analyzers in the flue gas ductwork can help operators keep the furnace balanced, and prevent many problems.

Flue Gas Stratification Tells a Story
Forward-thinking operators will use these varying O₂ indications as a diagnostic tool to look for problems in the furnace, such as:

• Fuel Gas BTU variation – will be indicated by both O₂ and CO variation.
• Fouled burners – depending on the consistency and quality of fuel burned in a furnace, a burner will change over time.
• Flame carryover – combustion sometimes progresses well into and beyond the convective zone, and is indicated by lower O₂ readings, higher CO readings, or both, along with rising outlet temperatures.
• Tube leaks – an unbalanced furnace can cause flame impingement and associated tube wastage.
• Furnace casing leaks – will result in elevated O₂ readings, since 21% of the air leaking in is oxygen.
• Sticking dampers – stack outlet dampers are sometimes poorly maintained, and sluggish control of O₂, COe, and furnace draft are indicative of problems.

Combustion flue gas analyzers have become true analytical tools for determination of all kinds of furnace problems. We’ll talk about others in future blogs.

For more information on this subject, please visit the following links:

• Flue Gas Analysis as a Diagnostic Tool for Fired Process Heater Furnaces Application Note
• Flue Gas Analysis as a Furnace Diagnostic Tool PowerPoint
• Flue Gas Analysis as a Furnace Diagnostic Tool ISA paper
  

Hello, I’m Michael Kamphus, application engineer for Process Gas Analyzers at Emerson Process Management, and today’s topic is the measurement of harmful gases that impact climate change and the technology used to control these.

As seen in the latest IPCC (Intergovernmental Panel on Climate Change) reports, CO₂, CH₄ and N₂O gases have the biggest effect on global warming. In addition to the previous, the EPA (US Environmental Protection Agency) also lists HFCs, PFCs, Halocarbons and SF₆ gases as major contributors to air pollution and global warming. Today, international agencies and governments are enforcing stronger emission regulations of these gases and willing to issue strict penalties and steep fines to those who do not comply. Technological advancements in today’s process gas analyzers have allowed gas processing plants, refineries, and others alike to safely measure, analyze, and closely monitor greenhouse gases in order to adhere to emission standards and protect the environment.

Rosemount Analytical, a business unit of Emerson Process Management, continues to lead the way in providing refineries, plants, and gas processing centers with the expertise and technology to accurately measure these greenhouse gases and remain compliant with today’s emissions standards.

The following are two examples of successful installations of Rosemount Analytical process gas analyzers monitoring greenhouse gas emissions:

Most of the industrial N₂O emissions come from nitric acid plants, many of which produce fertilizer. After oxidation of NH₃ to NO, NO reacts with water to form nitric acid, N₂O is a byproduct of the oxidation reaction. Special catalytic reactors can be implemented to eliminate the N₂O gases from nitric acid plant emissions. Measurement of flow and N₂O concentration behind the reactors are regulated by UNFCC (United Nations Framework Convention on Climate Change) within CDM (Clean Development Mechanism) projects. Both measurements need to be performed with QAL1 certified equipment. QAL1 is part of the European Continuous Emission Monitoring regulation. Rosemount Analytical N₂O gas analyzers now have a new QAL1 certification providing exceptional accuracy helping to earn carbon credits from N₂O emission reduction. Currently there are installations all over the world including Egypt, South Korea, South Africa and Chile. Recently, a major global engineering company partnered with Emerson Process Management to help control an N₂O abatement reactor and provide a complete turnkey solution which includes the installation and startup of temperature transmitters, pressure transmitters, flow transmitters, valves, gas analyzers and DCS systems to provide plant control and data reporting.

Other successful installations are in Australia, where the government has introduced carbon tax for emissions of greenhouse gases from coal mines. Therefore CO₂ and CH₄ have to be measured. A coal mine can pay up to $10M in carbon tax and a high-accuracy analyzer can help to reduce tax payment uncertainty. Rosemount Analytical worked with an Australian OEM company to successfully install high-accuracy process gas analyzers in flame-proofed housings for two separate applications: the first – to measure CH₄, O₂, CO and CO₂ in the tube bundle system for underground ventilation control and safety monitoring; the second, measure CH₄ and CO₂ from the exhaust of underground coal mines.

What kinds of harmful gases does your plant need to measure? What challenges do you face in that measurement?

Hi there. Michael Kamphus here. I’m an application engineer for process gas analyzers here at Emerson and in this blog post I’d like to discuss how the measurement of gas purity plays an important role across multiple gas processing industries and applications, mainly for the purpose of detecting gas impurities across a particular process. For example, in chemical reactions, one has to ensure the gases are free of carbon monoxide (CO) because of the risk of poisoning precious catalysts, oxygen (O₂) might oxidize catalysts, and carbon dioxide (CO₂) might form carbamates or carbonates which may clog process gas lines and lead to costly repairs.

One of the most important gas purity processes is the production of syngas, which is a mixture of CO and hydrogen (H₂) and used as a starting point for H₂ or CO generation. Syngas is mostly produced by steam reforming of natural gas. After the initial reformer, different reaction steps are necessary to convert and clean the process gas to achieve syngas in the desired H₂/CO ratio. Besides steam reforming of natural gas, other technologies generate syngas from coal gasification or wood/biomass gasification. The fertilizer industry uses syngas to produce ammonia and urea. Additionally, methanol and other hydrocarbons can be synthesized by the Fischer-Tropsch reaction, an access to liquid hydrocarbons independent from crude oil.

In air separation units, the inlet air has to be free of hydrocarbons (HC) and CO₂. After separation of nitrogen (N₂), O₂ and argon (Ar) has occurred, the product gas streams have to be monitored for impurities such as moisture, CO₂, HC and O₂, to ensure product quality. These gases and gases from other industrial processes are then used for gas bottling. Bottled gasses are needed in the food and beverage industry with the carbonization of beverages, welding and shielding to improve weld characteristics, and even in medical gases.

Emerson Process Management, Rosemount Analytical offers solutions for even the most challenging gas purity applications in refineries, fertilizer plants, steel plants and gas processing facilities around the world. For example:

• The impurity measurements of CO and CO₂ are done with non-dispersive infrared photometer (NDIR) measurements and detect from 0-10 ppm or 0-5 ppm, respectively.
• NDIR is also used for purity measurements of CO₂ and nitrous oxide (N₂O) with a max suppressed range of 98-100%. Hydrogen measurements are done with a thermal conductivity detector (TCD) making it possible to measure the H₂ purity up to 98-100% or impurities of H₂ in CO down to 0-1000 ppm.
• NOx, meaning the sum of nitric oxide (NO) and nitrogen dioxide (NO₂) measurements, are performed with a chemiluminescence detector (CLD) as a standard. These ranges can get down as low as 0-5 ppm.
• Hydrocarbon impurities are detected with a flame ionization detector (FID) with the lowest range being 0-1 ppm.
• Oxygen, as low down a range as 0-1%, but also suppressed ranges of 20-22% and 98-100%, can be measured with a paramagnetic sensor (pO₂). For O₂ ranges down to 0-10 ppm, a trace oxygen sensor (galvanic fuel cell) is used.
• For H₂O an aluminum oxide (Al₂O₃) based trace moisture sensor is integrated into the analyzer enabling us to deliver measurements on the dew point range from -100°C to -10°C or 0-100 to 3000 ppm.

The integration of different technologies can be combined into one analyzer housing; for example, a suppressed 98-100% O₂ purity measurement with a 0-10 ppm CO and a 0-5 ppm CO₂ impurity measurement, reducing cost for analytical equipment and making integration of the analyzer into the DCS much easier.

If you have a challenging gas purity application, have a question about process gas analyzers, or would like to share your experiences within the gas purity and process gas industry, we would like to hear from you. Post a comment and let us know!

To learn more about gas purity applications and process gas analyzers, visit www.rosemountanalytical.com/gaspurity.

Professionals in the oil and gas industry are continually dealing with energy expressions. The Wobbe Index may be a frequent reference, but most people can’t quote you the Gross BTU of propane off the top of their heads or give you a precise definition of Inferior Heating Value. That’s why the Analytic Experts at Rosemount Analytical are bringing you a Review of Gas Energy Expressions in today’s blog. Check it out, save it, print it. It’s your handy reference guide.

Gross Heating Value (also referred to as higher heating value [HHV]): The heating value (Btu) produced by combustion at constant pressure with the following conditions:

(a)    a volume of one cubic foot

(b)   60° Fahrenheit

(c)    reference base pressure

(d)   with air and gas having the same temperature and pressure

(e)   recovered heat from the water vapor formed by combustion

Net Heating Value (also referred to as lower heating value [LHV]): The heating value produced under conditions similar to gross heating value conditions excepting the amount of heat potentially recovered from the water vapor produced at combustion. Net heating value is always less than gross heating value.

The Relationship of Gross Heating Value and Net Heating Value

• The hydrocarbons combine with oxygen during combustion and these reactions provide the heat. When the hydrogen combines with oxygen, it forms water in a gaseous or vapor state at the high temperature of the combustion. The resulting formation of water is mostly carried away with the other products of combustion in the exhaust gases from the equipment where the gases are combusted (calorimeter, boiler, furnace, etc.). When the exhaust gases cool, the water will condense out and transform into a liquid state and release heat, known as latent heat, which is wasted in the atmosphere. The heating value of a fuel may be expressed as a gross value or a net value.
• The gross heating value includes all of the heat released from the fuel, including any carried away in the water formed during combustion.
• The net heating value excludes the latent heat of the water formed during combustion.
• The differences between gross and net heating values are typically 10% for natural gases, solid and liquid fuels.
• There are a few fuels that contain little or no hydrogen (for example, blast furnace gas, high-temperature cokes and some petroleum cokes). In these cases there will be negligible differences between gross and net heating values.
• The net calorific value of a process stream gas is the total heat produced by complete stoichiometric combustion, less the heat needed to evaporate the water present in the gas or produced during its combustion.

Relative Density: The ratio of the density of a gas to the density of dry air under the same pressure and temperature conditions (it’s sometimes referred to as specific gravity), relative to 1.0000 (air).

CARI value: Combustion air requirement index, the amount of air required for complete stoichiometric combustion of the fuel. CARI directly relates to Wobbe. It is the most common value used for air/fuel control.

Wobbe Index: The ratio of the gross heating value of a gas to the square root of the relative density of the gas (WI = Hv /Ö RD).

• Wobbe Index is a measure of the amount of energy delivered to a burner via an injector (orifice). The energy input is a linear function of Wobbe index.
• Two gases differing in composition but having the same Wobbe Index will deliver the same amount of energy for any given injector/orifice under the same injector pressure. 
• In natural gas appliances, the gas flow is restricted by passing it through an orifice (hole). The Wobbe Index is useful because for any fixed orifice size and gas pressure, any gas compositions that have the same Wobbe number will deliver the same amount of heat energy or expressed as interchangeability of varying gas compositions.
  

  Calculations of Specific Gravity, Calorific Value & Wobbe Index Table Excerpted From The Institute of Gas Technology, bulletin No. 32