Method for continuously monitoring chemical species and temperature in hot process gases

Abstract

Methods and apparatus are presented using tunable diode lasers for monitoring and / or controlling a high temperature process using an oxidizer containing O2 and organic fuel. Real-time monitoring of key species such as O2, CO, and H2O allow determination of the global or local stoichiometry, gas temperature, particulate concentration, and air entrainment levels into the process. Coupling the measured information with a control system provides a means for optimizing and controlling the process.

Description

[0001] 1. Field of the Invention[0002] This invention relates to the field of combustion. In particular, the invention relates to continuously monitoring the concentration of reactants, intermediates, or products from or in high temperature combustion processes. In addition, measurements on the process gas temperature, particulate concentration level and air entrainment rates can be obtained.[0003] 2. Related Art[0004] Numerous instrumentation choices are available for gas composition monitoring on industrial combustion processes operating at high temperatures (T>500.degree. C.). In particular, diagnostic instrumentation is useful for analysis of key combustion species such as O.sub.2, CO.sub.2, CO, NOx, etc. and using the measurement information for optimizing and controlling the process to improve energy efficiency, product quality, and minimize pollutants. However, high temperature and high particulate densities typically found in industrial processes limits the available moni...

AI Technical Summary

Benefits of technology

[0060] For the introduction of O.sub.2 into the gas stream, the O.sub.2 content can range from air to pure O.sub.2. However, to insure complete reaction of the gases and minimizing dilution effects O.sub.2 purity>90% is preferred. In addition, the same strategy can be applied to CO monitoring. Here, CO in a high temperature gas such as combustion flue gas reacts with injected O.sub.2 forming CO.sub.2. The CO.sub.2 can then be monitored using a near infrared laser in the 1.5 .mu.m spectral region. Comparison between the CO.sub.2 observed before O.sub.2 injection and after O.sub.2, injection provides an indirect means for measuring CO.

Problems solved by technology

However, high temperature and high particulate densities typically found in industrial processes limits the available monitoring methods to extractive sampling techniques.

All of these commercially available analyzers also exhibit a characteristic response time that will add to the measurement delay.

However, these instruments sample the gas in a batch mode with a slow response time ranging from approximately 30 seconds to several minutes depending on the GC operating conditions.

Discrete sampling and slow instrument response time hinders the ability to use the acquired information in a process control loop, particularly for processes with dynamic behavior.

However, the resulting mass spectra obtained are difficult to interpret due to overlapping fragments of ionized molecules having the same atomic mass.

Variations in the sampling flow rate, e.g., due to plugging or pressure fluctuations in the process itself, will change the response of the detector resulting in a measurement error.

However, in high particulate processes or in reducing environments plugging of the probe surface results in measurement degradation.

In addition, on processes that can have large thermal cycles as experienced in batch processes thermal shock of the ceramic probe can occur resulting in permanent damage.

However, these techniques suffer due to the complexity of the optical equipment needed and to date have been restricted to well controlled environments.

Mid-infrared diode lasers (2.5-25 .mu.m) require cryogenic cooling and are not easily coupled to fiber optic components, making the devices cumbersome for industrial applications.

Since diode lasers cover a broad wavelength range the limitations for detecting a specific species is dictated by the physics of the absorption process.

While other species that are infrared active have limited use due to weak absorption transitions and / or interference by other species in the measurement volume.

Images