Tunable Diode Laser Spectrometers

Tunable Diode Laser Spectrometers (TDLS) are laser-based gas analyzer which provide a fast-update optical analysis. The TDLS line offers measurements for process gas, flue gas, impurity analysis, custody transfer, safety, with in-situ and extractive methods supported.

In the chemical, power and refining industries, Yokogawa TDLS technology is acknowledged in a 2012 EPRI research study and the API 556 standard as the technology required for safe and environmentally responsible combustion applications.

  • The TDLS220 is specifically designed for accurate, reliable and low maintenance measurement of volume percent (vol%) oxygen (O2) for safety and process applications. It is a viable alternative to paramagnetic O2 analyzers.

  • Yokogawa’s new TDLS8000 houses all of the industry’s leading features in one robust device. The platform design is for in situ measurements which negates the need for sample extraction and conditioning.

The TruePeak Tunable Diode Laser Spectrometers operate by measuring the amount of a laser light that is absorbed as it travels through the gas being measured. Involving no sensor contact with the process and no moving parts, it leads to a high mean time between failures (MTBF) and hence a low long term cost of ownership (LTCO).

Fired heaters are integral to industrial processes, including hydrocarbon processing and power generation. Specifically designed for the reaction of fuel and air to produce extremely high gas temperatures, heaters transfer this energy to potentially highly flammable process fluids via heat exchangers. They consume large quantities of fuel, produce large quantities of emissions and are a potential safety hazard to personnel and plant.

Yokogawa TDLS analyzers help control fired heater combustion with ever greater accuracy and reliability. There are measureable rewards for operating fired heaters at Low Excess Air (LEA) levels. In LEA combustion control, the lowest level of fuel is consumed and the products of combustion are cooled the least by unused excess air.

The cost benefits of these efficiencies are considerable, with just a single percentage saving in fuel enabling savings of tens or even hundreds of thousands of dollars per year. Controlling air levels just above the point at which incomplete combustion starts also enables the "cleanest burn," helping plants meet environmental emissions requirements. This in particular reduces the emission of NOx.

Overview:

Electrolysis plants create hydrogen and chlorine from a brine solution. Chlorine gas generated from the anolyte of the electrolysis tank generally contains between 0.5 to 2.0 vol% H2O. The sample is then cooled and filtered to remove brine, subsequently coming out as wet chlorine gas. The wet gas is sent to a drying tower where it is treated with sulfuric acid to get moisture down to the ppm level. 

Overview:

The ammonia (NH3) gas is injected to remove the NOx and thus reduce the NOx concentration in the stack flue gas. With conventional NH3 analyzers that perform measurements indirectly, NH3 concentrations are obtained through a sampling system. Therefore, there are problems with the maintenance and running costs of the sampling system, and time delays in measurement. The TDLS200 Laser Analyzer is the solution to all these problems.

Industrias:
Overview:

En el mantenimiento y la administración de plantas industriales, monitoreo del pH de las aguas residuales / ORP es a la vez una obligación legal y una necesidad necesaria para la protección del medio ambiente. El Monitoreo sin estar atento puede llevar a consecuencias graves.

Industrias:
Overview:

Tomando en cuenta las cuestiones ambientales y de seguridad tales como la eficiencia de combustión y la disminución de NOX y CO en los gases de escape, se ha vuelto importante para controlar la concentración de O2 en los procesos de incineración de basura.

Overview:

Es necesario el manejo de H2S del gas de escape en calderas de recuperación de lejía negra para cumplir con las normativas ambientales.

Medios de Comunicación
Overview:

Tunable diode laser analyzers optimize combustion through direct measurement of O2, CO and methane.

Overview:

Spectrometric technology can assess many critical characteristics about products, but it has limits. It can be challenging to determine when the line has been crossed

Industrias:
Overview:

SABIC is a global manufacturer of polymer resins, film and sheet products, special additives, and chemical intermediates. With operations in more than 50 countries, the company has an enormous variety of processes and plant designs to make its range of products. With so many plants, processes and products, there are frequent opportunities to make improvements with hardware and instrumentation.

A case in point is a reaction process in which oxygen gas is sparged into the reactor, and there is a resulting outlet gas stream. Proper and timely measurement of the oxygen content in this outlet stream is of key importance for reaction control and safety. Reaction progress, control of raw materials input, and reaction sequencing are all affected and dependent on the value of the oxygen concentration reading. The reactor contents and outlet stream can also be in the flammable range depending on conditions, so safety and process considerations call for continuous monitoring of the vent line contents.

A Two-Fold Measuring Function

The safety considerations of monitoring oxygen content in the vent line are very important. As long as the oxygen level remains below a limit, the mixture can be kept below the flammable range and will not undergo combustion. If the process allows the concentration to exceed this limit, it shuts off the oxygen flow to the sparging headers. But this safety consideration is only one of the reasons the measurement is important.

Secondly, the amount of oxygen bubbling through the liquid is an indicator of what is happening in the reaction. Oxygen consumption depends on reaction chemistry and it is a direct indication of the status of the process. Accurate reading of overhead oxygen content is especially important for control of reactant addition and temperature control.

The Challenges of Consistent Measurement

Technologies to measure oxygen in a gas stream are not new, and there are countless applications in chemical manufacturing and other industries where oxygen levels need to be monitored. Combustion processes of any size invariably use some type of oxygen sensor in the flue gas stream to maintain efficiency.

SABIC’s situation proved to be more challenging than most typical applications due to a mix of specific conditions. For many years operators struggled while working with paramagnetic and electrochemical cell sensors due to degradation of the cells, moisture and debris from the process. These sensors are both very common and used in a wide variety of oxygen measuring applications, but they have some key limitations that became apparent when reviewing this process.

Paramagnetic analyzers are sensitive to vibrations and cross-contamination from other gases. Although the application for these reactors does not call for measuring trace amounts of oxygen, there are also sensitivity issues at very low concentrations. Electrochemical cells should be replaced routinely and have sensitivity to different pressures, temperatures and cross-contamination.

Our sampling systems experienced high failure rates with electrochemical components including sampling lines being plugged from the process, filter element clogging, and failing pumps. Moreover, since an individual test during production took more than two minutes, a possibility existed that a climbing oxygen level may not be identified soon enough.

Paramagnetic and electrochemical cell oxygen analyzers have a three-month verification frequency, and the manufacturers recommended maintaining this regimen precisely. Although the testing does not take long, production was delayed in some situations while performing the verification. Delays and Emergency work due to the failures of these types of analyzers resulted in a significant amount of lost production. Due to these and other issues, a more robust oxygen analyzer technology was required.

Tuning in to Laser Technologies

One technology used commonly in combustion processes is tunable diode laser (TDL) spectroscopy, capable of detecting and measuring a variety of gasses, including oxygen, within many contexts. Theoretically, it has the capability to measure oxygen when mixed with toluene, but there was some concern about it being practical for this specific application.

A TDL analyzer sends a beam with a controlled wavelength range through the gas being analyzed to determine which products are present based on which specific wavelengths of light are absorbed. The problem in this case related to the duct size, because the transmitter and receiver should be a minimum distance apart to ensure adequate absorption.

The duct diameter here was less than half the normally recommended distance, so there was some concern as to whether it would deliver its full degree of accuracy, or even work at all. SABIC’s engineers felt the potential benefits to be gained were more than enough to justify installing one analyzer as a test. The performance would be easy to evaluate since the existing sensors were still fully operational and working in parallel.

After two weeks of operation, it was clear the Yokogawa TDL analyzers were performing very well (Figure 1). It was true that they were not delivering the full degree of precision they were capable of due to the short scanning distance, but the precision was high enough to satisfy the needs of the process.

Figure 1. While the duct size for this application was smaller than is usually recommended for TDL analyzers, the tunable diode lasers reliably provided readings with a high enough degree of accuracy for the application, while eliminating the maintenance problems associated with the earlier sensing technologies.

Once installed, the new analyzers proved very reliable and required far less validation and maintenance than the earlier technologies. One issue proved to be debris carried into the duct from the process blocking the light transmission path between the transmitter and receiver. Adjustments to a nitrogen purging system and better control of the process itself minimized this effect, leading to virtually trouble-free operation.

Facilitating the Safety Function

All of these TDL analyzers have been installed for over two years now, with no failures due to the TDLA’s to date. Some units were outfitted with the Yokogawa TDLS200 analyzer, while others were outfitted with the Yokogawa TDLS8000 models. There are other manufacturers of this technology but we chose Yokogawa for this application.

There have been occasional visibility blockage incidents, but these are rare after adjustments to the purge system. Overall, these TDL analyzers have supported higher levels of production, and added another layer of protection to the unit.

Medios de Comunicación
Overview:

With fired heaters, users hope to get greater efficiency and reduced emissions but often are disappointed. Given the number of fired heaters operating every day and their importance in the process industries, any improvements realized across the board will have huge impacts. More units can reach their potential with some simple changes in work practices and technology upgrades.

Yokogawa Technical Report
Overview:

In recent years, shale gas extraction technology has made rapid progress, inducing a shale gas revolution mainly in the USA. Thus, the need for analysis of hydrocarbon gases, including natural gas, is expected to grow rapidly. Traditionally gas chromatography has been used for the analysis of hydrocarbon gases; it can accurately measure the concentration of each hydrocarbon component in a sample of natural gas.

Overview:

Combustion furnaces such as heating furnaces and boilers in plants include various sizes and types, and serve as energy sources, that is, they are cores in all production activities. Because a large amount of fuel such as gas or fuel oil is consumed in plants, their combustion efficiency directly affects the performance and running cost of the plants. 

Casos de Éxito

    Overview:

    Yokogawa Advanced Solutions recently sat down with László Cserna, Senior Project Manager at MOL Group where together we recently implemented the Yokogawa CombustionONE Furnace Optimisation Solution.

Webinars

    Overview:

    This webinar will explain the theory of operation of tunable diode laser spectrometers and the application thereof to gas fired reformers, boilers, & heaters as a layer of protection during startup and efficiency diagnostic during operation.

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