Improving Control and Efficiency of Waste Gasification

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Waste gasification utilizes waste material as the fuel in a waste to energy process, to create heat, electricity or other chemical products. The waste is decomposed in such a way so as to produce gaseous products, known as syngas: a combination of hydrogen, carbon monoxide and some carbon dioxide.1

In conventional incineration, heat and oxygen is used to combust waste products. Waste gasification on the other hand still requires high temperatures, but there is no oxygen. This produces fewer pollutants and no potentially toxic ashes. The syngas that results from the process is a valuable fuel either for steam and electricity production, or it may be used as chemical feedstock in the synthesis of more valuable products.2

Complex Processing

Although waste gasification is certainly much more attractive than conventional incineration, the processes in which the waste is broken down are complex and can be hard to optimize. The optimum conditions vary along with the chemical composition and moisture content of the waste feedstock, making it difficult to discern the point at which the most efficient waste to syngas conversion occurs.3    

The entire gasification process can be divided into several basic steps. First, remove oxygen, the waste is dried by heating so that pyrolysis can begin in an oxygen-free environment. The drying produces some vapors and char. Once the temperature gets high enough, the waste feedstock will begin to oxidize, in exothermic reactions that form carbon monoxide, water vapor and additional heat. This allows the process to be self-sustaining. There are also endothermic reduction reactions that produce the syngas of interest.

At the oxidation stage, a ‘gasifier’ or a chemical species must be introduced that enables the necessary chemical reactions to occur. Gasifiers may be introduced across a range of pressures and temperatures, and there are a number of suitable gases. This variation in the initial feedstock, range of input pressures and temperatures, as well as different gases, means that gas inputs and outputs must be monitored continuously if the efficiency of production is to be maximized.4

Gas Measures

Online gas monitors are one commonly used approach to ensure that optimal energy production values are maintained. These devices continually assess the levels of the gases produced in the syngas mixture or the input gas concentrations for oxidation.5 While gas may be collected at points for offline analysis, this can only be done at certain intervals, whilst also being more labor intensive and does not provide as comprehensive monitoring as a series of online monitors.

Being able to continuously monitor gas levels and adapt the process as the reaction proceeds is hugely beneficial.6 It is therefore fortunate that Edinburgh Sensors offers a range of products that are ideal for gas monitoring, data logging, and integrated applications.

Monitoring Options

For customers needing to detect both oxidation gas concentrations and the chemical composition of syngas, the comprehensive range of non-dispersive infra-red sensing instruments from Edinburgh Sensors is ideal. These devices are ideally suited for highly sensitive online monitoring of gases such as carbon monoxide and dioxide, and each one comes with pre- and post- sales and technical support to ensure that they match the customer’s needs exactly.

If the sensing is for CO or CO2, Edinburgh Sensors offers the Gascard NG7, the Guardian NG8, and the Chillcard NG9. While the Chillcard is designed for the monitoring of refrigerated gases, the Gascard NG and Guardian NG may be used for measurements in atmospheres of up to 1150 mbar of pressure and humidity conditions ranging between 0 – 95%.

If it is only CO2 sensing that is desired, then customers may prefer the GasCheck, a low-cost, robust device with a CO2 sensitivity of between 0 – 3000 ppm.10 Another option for CO2 sensing is the IRgaskiT. This compact device weighs just 125g, and offers a range of advanced integration possibilities with monitoring and feedback systems for process control.11

Simplicity and Sensitivity  

Two of Edinburgh Sensor’s most popular gas monitors offer impressive sensitivity for gas detection, almost the same as what can be achieved with offline analyzers. For even greater ease of use and installation, the GasCard can now be purchased as a pre-built desktop unit, the Boxed Gascard12.

GasCard NG from Edinburgh Sensors

GasCard NG

With detection ranges of 0–3000 ppm, up to 0–100% volume, and an impressive response time of less than 30 seconds from the sample inlet, the Guardian NG is an excellent gas detection solution. Possessing an accuracy of ± 2%, the Guardian NG can be relied upon to detect even the slightest of changes in gas concentrations.

There is also a display screen that outputs a live reading of both pressure and true volume percentage, as well as historical graphical data. For connecting to external devices, such as alarm systems or for external logging and monitoring purposes, both the Guardian and GasCard have a range of connections, with the GasCard having true onboard RS232 connections along with the option of TCP/IP communications protocols.

The Gascheck is based on analog electronics to give a zero-stability of ± 3% over 12 months, for CO2 detection in more demanding environmental conditions. Not only reducing the need for time-consuming collection and offline analysis of gases, the Gascheck’s robust design means that it can be depended on for consistently accurate logging without regular interference and recalibrations.  

No matter the volume or type of starting material used, these easy-to-install online gas monitors ensure that full control of the waste gasification process is maintained. They are the ideal devices for customers looking to achieve optimum energy conversion throughout continuous waste plant operation.

References and Further Reading

  1. U. Arena, Waste Manag., 2012, 32, 625–639.
  2. S. K. Gangwal and V. Subramani, Energy & Fuels, 2008, 22, 814–839.
  3. M. Saghir, M. Rehan and A.-S. Nizami, in Gasification for Low-Grade Feedstock, 2018, vol. 6, pp. 97–113.
  4. J. Gañan, A. A. K. Abdulla, A. B. Miranda, J. Turegano, S. Correia and E. M. Cuerda, Renew. Energy, 2005, 30, 1759–1769.
  5. Gas Analysis in Gasification of Biomass, https://www.ieabioenergy.com/wp-content/uploads/2018/09/IEA-Bioenergy-Task-33-gas-analysis-report-Document-1-1.pdf, (accessed February 2019)
  6. P. Kannan, A. Al and C. Srinivasak, in Gasification for Practical Applications, 2012, pp. 279–296.
  7. Gascard NG, https://edinburghsensors.com/products/oem/gascard-ng/, (accessed February 2019)
  8. Guardian NG, https://edinburghsensors.com/products/gas-monitors/guardian-ng/, (accessed February 2019)
  9. Chillcard NG, https://edinburghsensors.com/products/oem/chillcard-ng/, (accessed February 2019)
  10. Gascheck, https://edinburghsensors.com/products/oem/gascheck/, (accessed February 2019)
  11. IRgaskiT, https://edinburghsensors.com/products/oem/irgaskit/, (accessed February 2019)
  12. Boxed Gascard, https://edinburghsensors.com/products/oem/boxed-gascard/, (accessed February 2019)

This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.

For more information on this source, please visit Edinburgh Sensors.

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