75
Views
15
CrossRef citations to date
0
Altmetric
Original Articles

Coal Quality Impacts on Alkali Vapor Emissions from Pressurized Fluidized Bed Coal Combustors

, , , , &
Pages 229-247 | Received 05 Sep 2000, Accepted 15 Feb 2001, Published online: 05 Apr 2007
 

Abstract

This paper describes a modeling study that was undertaken to identify the major ways that coal quality affects alkali vapor emissions in PFBC exhaust systems. The central premise is that the impact of coal quality can be reliably evaluated from kinetically based predictions of the concentrations of NaCl, KC1, SO2. HCI, O2, and H2O in the exhaust from the bubbling bed in combination with ther-mochemical equilibrium relations for conversion of alkali chlorides into alkali sulfate fumes in the freeboard. This hypothesis was implemented in a PFBC simulator that accounts for the major aspects of coal combustion and sulfur capture, and includes several mechanisms for alkali transformations.

The model predicts a huge variation in exhaust Na vapor levels for different coals, ranging from the ppm-level with low rank coals to tens-of-ppb with hv bituminous coals for realistic levels of in-bed sulfur capture. This range is consistent with measured Na vapor emissions from two laboratory-scale systems. Hence, this approach exhibits the potential to predict Na-vapor emissions within useful quantitative tolerances at temperatures above 900°C with any coal type that contains sufficient chlorine to shift all alkali vapors into their chloride forms. It also demonstrates that the impact of all the coal properties that affect alkali vapor emissions can be expressed in terms of only two primary variables, the SO2 and HCI concentrations in the exhaust after the alkali sulfate fume has formed. Whereas the essential connections among alkali vapor emissions and the concentrations of alkali vapors. SO2, and HCI are not widely recognized, this study identified a complete set of test conditions that are essential elements for stringently evaluating predicted alkali levels. Simultaneous measurements of alkali vapors, SO2, and HCI are the most important data requirements, together with the Na-, K-, and Cl-levels in the test coals and accurate measurement of the temperature and cooling rate at the sampling point.

Additional information

Notes on contributors

S. NIKSA

Corresponding Author: Stephen Niksa, Niksa Energy Associates, 1745 Terrace Dr., Belmont, CA 94002 (650) 654 3179 (Fax); [email protected]

Reprints and Corporate Permissions

Please note: Selecting permissions does not provide access to the full text of the article, please see our help page How do I view content?

To request a reprint or corporate permissions for this article, please click on the relevant link below:

Academic Permissions

Please note: Selecting permissions does not provide access to the full text of the article, please see our help page How do I view content?

Obtain permissions instantly via Rightslink by clicking on the button below:

If you are unable to obtain permissions via Rightslink, please complete and submit this Permissions form. For more information, please visit our Permissions help page.