ITP Forest Products Peer Review

Transcription

1 ITP Forest Products Peer Review Improved Recovery Boiler Performance through Control of Combustion, Sulfur and Alkali Chemistry PI: Larry Baxter, Brigham Young University R&D Partners: University of Maine University of Utah Chalmers/IPST INEL Industry Partners: Babcock & Wilcox, GP, Weyerhaeuser, IP

2 Technology Description Industrial Problem: Black liquor combustion lacks sufficient characterization in several areas that strongly impact recovery boiler operations, ultimately decreasing energy efficiency, throughput and availability of boilers. Project Goals: Determine black liquor drying, devolatilization, elemental and total mass release rates and yields. Develop a model of black liquor droplet combustion, including new information on drying and devolatilization. Determine mechanisms and rates of sulfur scavenging in recover boilers. Develop data and a one-dimensional model of a char bed in a recovery boiler. Implement combustion code and validate effects on boiler performance.

3 Energy Savings Potential Market: 1) Best Case Scenario All current and future mills adapt the control strategies being developed 2) 600 kraft pulp mills in the U.S.(stand-alone mill or part of integrated paper mills) 3) U.S. statistics based on total pulp production, there are 160 fullsize kraft pulp mills in operation producing 1000 ADT/ day of unbleached kraft pulp, based on 350 days per year 4) The strategies we develop should apply to all recovery boilers. Future Commercialization: 1) Commercial introduction control strategies should begin before this project is complete as we field test our assessments. 2) Total market saturation will depend on the success of the strategies but could occur in as quickly as 5 years.

4 Energy Savings Energy Savings: A decrease in the amount of sootblowing is assumed, with a concomitant effect on the amount of residual fuel oil consumed by the recovery boiler (the black liquor consumption is maintained in order to allow high process throughput). Fuel Type New Tech. Current Tech. Comments Annual Unit Energy Use (in physical units) Electricity (million KWh) Natural Gas (million cubic feet) Petroleum (million barrels) Steam Coal (million short tons) Black Liquor (thousand tons) Hog Fuel (thousand tons) Wood chips, bark *Assuming 33% decrease in soot blowing

5 Energy Savings Non-Energy Impacts (per unit-year of operation: Non-Related Emissions New Tech. Current Tech. CO 2 (expressed as metric TCE) Other greenhouse gases 3 3 (CH 4,HFCs,CFCs) SO NO x Particulates VOCs 6 6 Hydrocarbons 3 3 CO Toxic (TRI) (please specify) NA NA Hazardous (non-tri) (please specify) NA NA Non-Hazardous Solid Waste (RCRA) NA NA TRS 9 10 TCE = tons carbon equivalent (44 C0 2 /12 C)

6 Project Strategy-Milestones Date Milestone Completed Date Milestone Completed 12/15/03 Initial code for drying and devolatilization 6/16/03 Single droplet Experiments 6/16/03 Go/No Go Drying & Devolatilization work 12/15/03 Devolatilization experiments in LEFR/one liquor 12/15/04 Devolatilization experiments in LEFR/2 liquors 2/16/04 Experiments/Sulfur scavenging 7/15/04 Go/No Go sulfur modeling 11/15/04 Complete sulfur scavenging model 10/15/03 Complete publicdomain thermochemical code 6/17/03 Lab testing of Char Bed Burning 6/30/03 Construction of U Maine Char Bed Facility Unanimous Go 15% Unanimous Go 70% 7/15/04 12/16/02 10/15/03 4/15/05 12/16/02 4/15/03 11/15/04 4/15/05 4/15/05 7/15/04 6/15/06 Experimental Variables at U of Maine Char Bed Modeling of existing IPST devolatilization Detailed Model of Lab Char Bed combustion Complete modeling/algorithms of rates of Char bed Construction of probes and set ups for char bed/maine Initial char bed gas sampling/maine Char Bed Sampli ng/ Maine Simulation of char bed model Commercial Operation Simulation Incorporate particle model into comprehensive Final Report 10% 95% 7/31/03 Effect of temp. in the U. Maine Facility 7/15/02 Project/Gantt chart/ reporting schedule

7 Project Strategy Key Barriers: Interface between industry and research community. General decline in enthusiasm for pulp and paper mill investment. Overcoming Barriers: Develop models that require minimal user academic expertise. Help develop new products and directions for industry. Status of Milestones: The bed model originally to be developed at the University of Maine is now completed at BYU. The comparison of the now fully three-dimensional bed model at BYU (original proposal called for a onedimensional model) with measurements being made by University of Maine remains to be done. The University of Utah diagnostic development did not succeed. Otherwise all essentially complete. Commercialization Plans: One donated patent on related technology and is pursuing two additional patents related to laboratory devices. The donated patent has potential commercial application, albeit to gasification rather than combustion. The two patents under development relate more to laboratory measurements (pyrometry measurements using wide-band spectroscopy and droplet levitation using laser beams) than to commercial application. All software is intended for public use. Work with recognized modelers who place results directly into design and troubleshooting algorithms.

8 BL Particle Combustion Single-particle reactor (SPR)

9 BL Combustion Stages Drying Black Liquor is 15-35% H 2 O Drying Devolatilization Swells 1-2x original diameter Devolatilization Swells 3-5x original diameter Visible flame surrounding the particle Continual increase in temp Char Burning Smelt Oxidation Constant gas evolution Char Burning Longest stage Limited by mass diffusion Smelt Oxidation Oxidation of sodium potassium and their salts

10 Experimental and Model Results ) Temperature (ºC 52 mg Bl ack Liquor Droplet in Air Time (s) Experimental Temp Predicted Center Temp Predicted Surface Temp Experimental Mass Loss Predicted Mass Loss m/m Successes The sub-boiling temperatures are consistently predicted and measured. Following drying, the particles relatively rapidly heat, with heating rate predicted and measured to decrease during devolatilization because of the impact of the rapid convective losses on heat transfer coefficients. After the entire particle completes devolatilization, both center and surface temperatures rise much more rapidly than during devolatilization. Because of lower particle mass Fewer escaping gases increase heat convection The overall conversion time and the general shape of both the mass loss and temperature profiles generally agree.

11 Shape and Size Effects Effects of particle shape and size on conversion time Conversion Time Ratio AR=5.0, in N2 Near-sphere/Pl ate, exp Cyli nder/plate, exp Plate/Plate Near-sphere/Pl ate, model Cyli nder/plate, model Conversion Time Ratio AR=8, in N2 near-spheri cal/plate - exp. cylinder/plate - exp. plate/plate near-spheri cal/plate - model cylinder/plate-model plate/plate Sphere-equivalent Diameter, mm Sphere-equivalent Diameter, mm AR=5 AR=8 Wood particle, T w =1273 K, T g =1050 K

12 Color-band Temperature Measurement XY image XZ image ZY image 3D model 3-D surface temperature map of a biomass particle during combustion Surface temperature and emissivity of a black liquor drop during combustion

13 BL Combustion Conclusions 1. A comprehensive solid fuel particle combustion model has been developed for particle fuels with a variety of shapes and sizes, which better predicts biomass combustion than isothermal, spherical particle model. 2. Substantial temperature gradients exist in mm-sized particles. 3. Inorganic reactions contribute significantly to reactivity 4. Swelling strongly impacts mass loss rate 5. Near-spherical particles loose mass most slowly during combustion, consistent with theoretical analysis. 6. Data and theoretical models indicate that shape impacts increase with increasing size and increasing asphericity and are large at sizes relevant to black liquor utilization.

14 Single Particle Diagnostics A focused beam traps 5-25 μm particles Two major forces counteract gravity: 1) Photon force: Each incident photon transfers momentum equal to h/λ 2) Free convective drag force Free convective drag Laser heats particle, inducing convective flow Flow generates convective drag force Fluent TM predicts F drag as a function of dp and Tp Convective drag force is 90% or more of trapping force 5 mm

15 Drag Force Model vs. Data Comparison of Fluent predictions with experimental results of the freeconvective drag force (Mograbi & Bar-Ziv, 2005)

16 Application of Particle Diagnostics Establishing trapping mechanism allows us to develop novel, nonintrusive diagnostic tool Diagnostic may provide more accurate, cheaper, safer, and faster access to gas pressure and composition regimes previously difficult to study Possibly most significant is the possibility of studying reaction kinetics at gasification pressures and variable gas compositions Use size and temperature measurement algorithms developed within this research group

17 Acknowledgements Project Partners: Adriaan van Heiningen University of Maine Orono, ME Richard A. Wessel Babcock & Wilcox Barberton, OH Kevin Whitty University of Utah Salt Lake City, UT Brent Detering INEL Idaho Falls, ID Kristiina Iisa IPST Atlanta, GA 30318