Online Measurements of Alkali Metals during Start-up and Operation of an Industrial-Scale Biomass Gasification Plant

Abstract

Alkali metal compounds may have positive influences on biomass gasification by affecting char reactivity and tar reforming but may also disturb the process by formation of deposits and agglomerates. We herein present results from online measurements of alkali compounds and particle concentrations in a dual fluidized bed gasifier with an input of 32 MWth. A surface ionization detector was used to measure alkali concentrations in the product gas, and aerosol particle measurement techniques were employed to study concentrations and properties of condensable components in the gas. Measurements were performed during start-up and steady-state operation of the gasifier. The alkali concentration increased to approximately 200 mg m–3 when fuel was fed to the gasifier and continued to rise during activation of the olivine bed by addition of potassium carbonate, while the alkali concentration was in the range from 20 to 60 mg m–3 during steady-state operation. Addition of fresh bed material and recirculated ash had noticeable effects on the observed alkali concentrations, and K2CO3 additions to improve tar chemistry resulted in increased levels of alkali in the product gas. Addition of elemental sulfur led to reduced concentrations of CH4 and heavy tars, while no clear influence on the alkali concentration was observed. The study shows that alkali concentrations are high in the product gas, which has implications for the fluidized bed process, tar chemistry, and operation of downstream components including coolers, filters, and catalytically active materials used for product gas reforming.

Alkali Monitoring of Industrial Process Gas by Surface Ionization─Calibration, Assessment, and Comparison to In Situ Laser Diagnostics

“…The SI technique has been demonstrated in previous studies and applied in industrial applications, such as combustion, gasification, and chemical looping processes. ,,,, A detailed description of the methodology can be found elsewhere . In brief, the sample gas flows through a chamber with a hot metal surface, where a fraction of the aerosol particles impinges, decomposes, and desorbs as a result of the high temperature (typically ∼1500 K).…”

“…The test aerosol was generated with a constant output atomizer (TSI 3076), and the gas stream was diluted with nitrogen gas before being split and directed to the two instruments. A similar setup has been used in previous investigations, , and both the SMPS and atomizer are well-characterized commercial units. However, to convert the measured number concentration to a mass concentration, both the particle shape and density are required.…”

“…The physical properties of Pt (low oxidation potential and low work function) make it an ideal candidate for continuous alkali monitoring, although several different filament materials and geometries have been explored. A few different cell designs have been described. ,,,− The most common application uses a Pt spiral encapsulated in metal housing at room temperature and atmospheric pressure, where the sample gas is directed. To control the flow pattern and increase the amount of alkali particles that interact with the filament, different cell designs have been evaluated.…”

Mini-Review on Hot Gas Filtration in Biomass Gasification: Focusing on Ceramic Filter Candles

“…Both online and offline instruments had been used to characterize the nanosized aerosol PMs in the hot product gas from biomass gasification, ,, and particle size distributions with two distinct modes were established . The fine mode (15–140 nm, 640 mg/m 3 , 2 × 10 10 PMs/cm 3 ) was supposed to contain mainly heavy tars formed through a homogeneous nucleation and condensation on alkali nuclei; another intermediate mode (140–670 nm, 38 mg/m 3 , 4.3 × 10 6 PMs/cm 3 ) was assumed to be a mixture consisting of original PMs formed by condensed alkali vapors and tars from the gasifier .…”

Interactions between Kaolinite, Organic Matter, and Potassium Compounds at Elevated Temperatures during Pyrolysis of Caking Coal and Its Density-Separated Fractions

“…In addition, the organic potassium content in the caking coal evaluated in this study is 0%. Therefore, there is a need to understand the effects of the addition of low proportions of potassium compounds to fixed-bed gasifier feed coals for the mitigation of the severe caking of coal particles. ,,,, Potassium compounds can catalyze pyrolysis and gasification reactions, which are not part of the current study. ,,,, However, the addition of significant amounts of potassium compounds into a biomass gasifier has been shown to negatively impact the pyrolysis and gasification processes. , Excessive potassium compound addition resulted in inevitable plant burning issues, i.e., fouling, corrosion, deposit/agglomerate formation, and commercial products contamination. These researchers also investigated the behavior of potassium compounds in biomass gasification and their effects on the pyrolytic and gasification products.…”