TDL absorption sensors for gas temperature and concentrations in a high-pressure entrained-flow coal gasifier

Abstract

We report the first tunable diode laser (TDL) absorption measurements for gas temperature and species concentrations in a pilot-scale, high-pressure, entrained-flow, oxygen-blown, slagging coal gasifier with pressures up to 18atm and temperatures to 1800K. Three locations in the gasifier flow were investigated: (1) the reactor core, (2) the exit of the reactor where a water spray quenches the reaction products (pre-quench), and (3) in the gasifier product stream before particulate clean-up (post-quench). Gas temperature was measured by three pairs of H2O transitions with distinct temperature dependence at all three locations using five distributed feedback (DFB) lasers near 1.4μm. CO, CO2 and H2O concentrations were measured at the post-quench location using DFB lasers near 2.3μm, 2.0μm and 1.4μm, respectively. Fixed-wavelength, 1f-normalized, wavelength-modulation-spectroscopy with second-harmonic detection (WMS-2f) was used for all the measurements. Usable signal-to-noise ratio (SNR)>10 was achieved with one second averaging even at gasifier conditions with large particulate loading where the non-absorption transmission loss was >99.99% from light scattering and the thermal emission was intense. The work demonstrates the capability of TDL sensors to monitor transient changes in gas temperature providing a potentially valuable control sensor for gasifier performance. In addition, measurements of CO, CO2 and H2O in the gasifier product stream showed good promise for monitoring the syngas heating value. The potential advantages of using higher WMS harmonics under high-pressure conditions were also investigated.