WSRC-TR-2000-00099, Rev. 0

 

 

Literature Search for Off-Site Data to Improve
the DWPF Melter Off-Gas Model

W. E. Daniel
Westinghouse Savannah River Company
Aiken, SC 29808

 

This document was prepared in conjunction with work accomplished under Contract No. DE-AC09-96SR18500 with the U.S. Department of Energy.

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Executive Summary

A literature search was conducted to uncover data to help remove some of the conservatism built into the DWPF melter off-gas model in response to the DWPF Technical Task HLW-DWPF-TTR-00-0011, Rev. 0. Currently, feed to the DWPF melter is limited by an interlock on the minimum melter vapor space temperature to ensure adequate combustion and minimize the build-up of hydrogen. The melter vapor space temperature interlock value was set using the DWPF melter off-gas model, which was based on data obtained during the 9th Scale Glass Melter Campaign in 1989.

Unfortunately, the literature search did not turn up data that could be used to reduce the conservatism built into the assumptions for the melter off-gas model. Two articles were found that contained some off-gas data but either did not contain enough details and/or operating conditions were too dissimilar to DWPF to be useful. One of these articles was for a bench-scale melter (1.4 L glass volume) and the other was for the Liquid Fed Ceramic Melter both in support of the Hanford Waste Vitrification Plant project. Both of these melters were operated under research not production off-gas hydrogen constraints. Even though the data was not directly applicable to DWPF, it was hoped that it could provide some comparative basis on which to change some of the flammability model assumptions. After review by ITS and DWPF engineers, the articles did not provide data to refine the off-gas model.

Many different sources were utilized in performing the literature search and many articles concerning melter operations were found. The body of this report documents the sources used to perform the literature review and contains brief annotations of any relevant articles found. Some articles may be useful in other DWPF operations, such as the SRAT/SME cycles.

Future Work

To further expand the literature search performed for this task would require tracking down the researchers/experts in the field of melter/combustion off-gas and contracting their services. Another alternative would be to perform some melter studies in the pilot-scale melter coming to the Thermal Fluids lab. These melter studies could be designed to provide off-gas data to be compared with model predictions and to help refine the model. At the same time, the experimental data could be used to reduce some of the conservatism built into the off-gas model.

Background

This document is in response to DWPF Technical Task HLW-DWPF-TTR-00-0011, Rev. 0 to perform a literature search to uncover data to help remove some of the conservatism built into the DWPF melter off-gas model. Feeding to the DWPF melter is limited by many factors, one of which is the minimum melter vapor space temperature. An interlock is in place for the vapor space temperature to prevent a loss of combustion and thus potential build-up of hydrogen. The current DWPF melter operating settings are based on data obtained in 1989. Although the DWPF melter off-gas model has been updated since its original design, the assumptions that are part of the model limit such things as the minimum melter vapor space temperature.

This report documents the literature search performed and any relevant data that may help relax some of the constraints on the DWPF melter off-gas model.

Introduction

The objective of this task was to look for outside sources of technical data to help reduce some of the conservatism built in the DWPF melter off-gas model. The task was broken into two subtasks as described below.

Task 1 - Perform a literature search for data to augment the DWPF off-gas model
Task 2 - Evaluate any data found as it relates to the DWPF off-gas model

A variety of sources were searched for relevant information to melter off-gas and flammability. These references are discussed in the following section along with brief annotations of the various information found.

Discussion

Literature Searches

The majority of the literature searches were performed on-line using the Internet and our sites Intranet. The literature search was begun by a general search of the Internet using www.altavista.com. Keywords and phrases like off-gas model, melter gas model, and combustion gas model were used. None of these searches turned up any significant findings but led to other sources on-line, such as the Journal of American Ceramic Society Abstracts at www.ceramicjournal.org/. This on-line source, however, did not turn up anything.

The other on-line searches were performed using the EnergyFiles EnergyPortal Search at www.osti.gov/EnergyFiles. The EnergyFiles site provides information and tools to access a vast array of scientific resources pertaining to energy-related research. The site is maintained by the Department of Energys Office of Scientific and Technical Information (OSTI) under the Departments Scientific and Technical Information Program. The EnergyPortal search allows one to sepresentarch web-related sites along with multiple databases including: DOE Information Bridge, DTIC Technical Reports Database, DOE OpenNet Database, IBM Patents Database, DOE Reports Bibliographic Database, NASA CASI Technical Reports, DOE R&D Accomplishments, PubSCIENCE (prior to 1990), DOE R&D Project Summaries Database, and PubSCIENCE (1990 - ). There are also other field specific databases that may be searched including EPA Technical Reports, Environment Management Science Research Projects, and Electronic Resource Plutonium Library. The aforementioned databases were searched for any data relating to melter/combustion off-gas modeling and/or flammability. These searches covered hundreds of thousands of articles, reports, and abstracts. Of all the searches performed, only three articles were found that had data concerning melter off-gas similar to DWPF. However, no specific sources were found that directly address the key assumptions for melter off-gas flammability modeling. On the other hand, several articles were found that could possibly be used for other DWPF operations like melter feed preparation in the SRAT/SME and for general melter modeling. Any relevant data found during the literature search will be discussed in the next section which contains annotations from these articles.

SRTC library resources were also used to conduct the literature search. There is an on-line Index Search engine called WinSPIRS that allows one with a SRSDomain account to search the following indices:

All the above indices were searched for references to melter off-gas, flammability, and/or combustion modeling. No data matches were found to the DWPF melter but some articles were found discussing furnace and incinerator modeling. These articles will be highlighted in the annotation section next.

The SRTC library also had some links to on-line search engines under electronic journals that were used. The first is the Elsevier Journal search that has an advanced search engine at the link http://sciserver.lanl.gov/cgi-bin/search.pl/GetExpandedSearch. The other is the EBSCO search engine at the link http://www-us.ebsco.com/online/Reader.asp. The EBSCO search allows both journal and article searches. Both the Elsevier and EBSCI search engines were searched for references to melter off-gas, flammability, explosion limits, and/or combustion modeling. No relevant articles were found other than some references that appeared in the other on-line searches.

Annotated Search Results

Out of all the articles and documents reviewed, only three were found to contain data concerning melter off-gas. These three articles will be discussed next.

Feed Process Studies: Research-Scale Melter, K. F. Whittington, D. K. Seiler, J. Luey, J. D. Vienna, W. A. Sliger, PNNL-11333, September 1996.

This report discusses some Research-Scale Melter (RSM) experiments to examine processing rate, cold cap behavior, off-gas properties, and glass characteristics in support of the Hanford Waste Vitrification Plant project. Some off-gas data is presented along with a detailed breakdown of the cold cap by layers. The Research Scale Melter operates around 1150 C and has a general waste loading of 40% to 48%. The RSM feed is a slurry like DWPFs but has a slightly different composition, such as higher aluminum, boron, iron and lower silicon. An example RSM feed composition is shown in Table I. Some average properties of the RSM feed are shown in Table II. Since the PNNL melter feed is similar to DWPFs, a simple comparison of its off-gas data was made trying to take into account the scale of Research Scale Melter. A comparison of melter and off-gas data between DWPF and the PNNL RSM is shown in Table III. As can be seen in this table, the glass surface area to volume ratio is about the same in both systems but the feed to surface area ratio is much higher in the PNNL RSM than in DWPF. Another way of looking at this finding is the glass production rate per unit surface area, which is an order of magnitude higher for the PNNL RSM than DWPF. At the same time, the off-gas flow to feed ratio is much higher for PNNL RSM than for the DWPF melter. Note that the off-gas flow includes both supplied air and in-leakage air. The large air input to RSM is confirmed by the off-gas composition which is very much like that for air, more so than for DWPF. What this data does show is that DWPF is already pumping in less air per unit feed than the PNNL RSM. A better comparison could be made if the average feed to surface area ratio, the glass production to surface area ratio, and the off-gas flow to average feed ratios were closer. These close matches would allow better-scaled comparisons, as both melters would be operating on about the same basis even though different scales. In the PNNL RSM runs, hydrogen production was not a problem most likely due to the large amount of supplied air.

 

Table I.  Example RSM Feed Composition

Oxide

Wt% Oxide

Al2O3

8.89

B2O3

12.24

BaO

0.15

CaO

1.33

CdO

0.60

Fe2O3

13.13

K2O

0.02

La2O3

0.12

Li2O

1.22

MgO

0.53

MnO

0.40

Na2O

19.81

Nd2O3

0.44

NiO

0.34

P2O5

0.71

ReO2

0.23

SiO2

38.41

ZrO2

2.16

 

Table II.  RSM Average Properties

Property

Value

Denisty, g/ml

1.45

Wt% Solids

48

Wt% Oxides

38

PH

7.7

Oxide Loading, g/L

530

 

Table III.  Comparison of PNNL RSM with DWPF Melter

RSM

DWPF

Glass Volume

1.40 L

3200.00 L

Glass Surface Area

0.018 m2

28.27 m2

Glass Surface Area/Vol

0.013 m2/L

0.009 m2/L

Avg Feed

1.90 L/hr

204.00 L/hr

Avg Feed/Surface Area

104.40 L/(m2*hr)

7.22 L/(m2*hr)

Cold Cap Coverage

95%

80%-95%

Glass Prod

0.90 kg/hr

103.40 kg/hr

Glass Prod/Surface Area

49.45 kg/(hr*m2)

3.66 kg/(hr*m2)

Offgas Flow

11.31 kg/hr

81.65 kg/hr

Offgas Flow

308.68 scfm

2228.38 scfm

Offgas Flow/Avg Feed

5.95 kg/L

0.40 kg/L

H2 vol%

<0.0033%

0.0017%

O2 vol%

21.01%

14.14%

N2 vol%

77.85%

83.44%

CO vol%

0.0046%

0.10%

CO2 vol%

0.41%

1.63%

NOx vol%

0.78%

0.055%

 

HWVP Pilot-Scale Vitrification System Campaign LFCM-8 Summary Report, J. M. Perez, L. D. Whitney, W. C. Buchmiller, J. T. Daume, G. A., Whyatt, PNNL-11096, April 1996.

This report covers some experiments in a Liquid-Fed Ceramic Melter (LFCM) that was suppose to be about one-half scale of the DWPF melter (200 L/hr feed). However, the tests performed in these experiments were only able to achieve a feed rate of 60 L/hr at 1150C. Higher feed rates of 80 L/hr were only sustainable at higher melter temperatures of 1200C. A good bit of off-gas data is shown for the LFCM runs but no basis is given for the choices of off-gas air flow, i.e. is it for 1x, 2x, or 3x gas surges. The LFCM feed is a slurry mix like DWPFs and has a very similar composition as shown in Table IV. Some average properties of the LFCM feed are shown in Table V. Since the LFCM melter feed is similar to DWPFs, an attempt was made to compare its off-gas data to that of DWPF. A simple comparison of the melter and off-gas data between DWPF and the LFCM is shown in Table VI. Unfortunately, not all the data was available to make a full comparison between the two systems. However, if one were to scale the LFCM values by the ratio of DWPF to LFCM feed rate, the results would look like that shown in column two of Table VI. The scaled LFCM production rate is comparable to DWPFs but the scaled off-gas flow rate is only half of DWPFs. This finding is supported by the off-gas composition for the LFCM where the hydrogen content is 100 times greater than that for DWPF, i.e. there is less air flow coming into the LFCM. This finding could be interpreted that less air flow is possible in DWPF while still staying below the lower explosion limit. For the LFCM experiments, the hydrogen concentration was 10 times smaller than the LEL. However, the LFCM and other research melters do not have to operate under the production requirements of DWPF where the operating conditions are based on a 3x surge in melter off-gas remaining less than 60% of the LEL of hydrogen.

 

Table IV.  LFCM Example Feed Composition

Oxide

Wt% Oxide

Al2O3

2.74

B2O3

14.03

BaO

0.05

CaO

0.24

CdO

0.98

Fe2O3

8.16

K2O

0.07

La2O3

0.19

LiO2

5.0

MgO

0.11

MnO2

0.64

Na2O

7.60

Nd2O3

1.00

NiO

0.66

P2O5

0.36

ReO2

--

SiO2

52.21

ZrO2

4.35

 

Table V.  LFCM Average Properties

Property

Value

Denisty, g/ml

1.31

Wt% Solids

40.8

Wt% Oxides

--

PH

--

Oxide Loading, g/L

450

 

Table VI.  Comparison of LFCM with DWPF Melter

LFCM

LFCM scaled

DWPF

Glass Volume

--

--

3200.00 L

Glass Surface Area

--

--

28.27 m2

Glass Surface Area/Vol

--

--

0.009 m2/L

Avg Feed

60.00 L/hr

204.00 L/hr

204.00 L/hr

Avg Feed/Surface Area

--

--

7.22 L/(m2*hr)

Cold Cap Coverage

--

--

90%

Glass Prod

25.00 kg/hr

85.00 kg/hr

103.40 kg/hr

Glass Prod/Surface Area

--

--

3.66 kg/(hr*m2)

Offgas Flow

11.90 kg/hr

40.46 kg/hr

81.65 kg/hr

Offgas Flow

--

--

2228.38 scfm

Offgas Flow/Avg Feed

0.20 kg/L

--

0.40 kg/L

H2 vol%

0.2000%

0.0017%

O2 vol%

--

14.14%

N2 vol%

--

83.44%

CO vol%

0.1000%

0.10%

CO2 vol%

2.0000%

1.63%

NOx vol%

0.2000%

0.055%

 

Detailed Design Data Package: Item 3.1a Film Cooler Pressure Drop Data; PHTD Pilot-Scale Melter Testing System Cost Account Milestone 1.2.2.04.15A, G. A. Whyatt, L. D. Anderson, J. Evans, II, PNNL-11045, March 1996.

This report contains data from testing the Liquid-Fed Ceramic Melter (LFCM) off-gas system for surges from melter feeding. The feed surges were simulated by injecting steam into the melter plenum to represent a seven-fold increase in steam generation. The report was examined to see if it provided any insight into the air supply settings for the DWPF off-gas film cooler. Unfortunately, no helpful information was found. A summary of the reports data is shown in Table VII.

 

Table VII.  LFCM Off-Gas Film Cooler Summary Data

Melter Air Flow, scfm

Plenum Temp, C

Plenum Press, psia

Film Cooler Air Flow, lb/hr

Film Cooler Exit Temp, C

Film Cooler Press Drop, inwc

Off-gas Line Press Drop, inwc

Case

58

706

14.15

812

308

2.1

3.6

Normal

58

562

14.26

762

363

11.6

14.4

Surge

41

774

14.22

908

308

2.1

3.8

Max Plenum Temp

 

The remaining articles reviewed did not contain any data directly related to DWPF melter off-gas modeling but may include information that may be useful for other DWPF operations. Brief annotations immediately follow for these articles.

Melt Rate Predictions for Slurry-fed Glass Melters, C. J. Freeman, PNNL-11012, March 1996.

This report presents a cold cap thermodynamic model and how certain terms such as thermal conductivity and heat capacity were derived from experimental data. The cold cap model is basically an energy balance over several layers between the melt pool and the vapor space.

Compilation of Information on Melter Modeling, L. L. Eyler, PNNL-11015, March 1996.

This report reviews melter modeling packages like CFDS FLOW-3D, FLUENT, FIDAP, STAR-CD, CFD 2000, and PATRAN. There are not a lot of details in this report but it does provide an overview of the modeling packages available in 1996.

Review of Three-Dimensional Mathematical Modeling of Glass Melting, R. Viskanta, Journal of Non-Crystalline Solids, vol. 177, pp. 347-362, 1994.

This article reviews current three-dimensional models for simulating flow and heat transfer in glass melting furnaces. Some sample flow and thermal profiles are also presented. The review is mainly aimed at gas/combustion furnaces and not joule-heated melters.

Modelling of Combustion and Heat Transfer in Glass Furnaces, Charles J. Hoogendoorn, Lourens Post, and Jan A. Wieringa, Glasstech. Ber., vol. 63, pp.7-12, 1990.

This paper presents a three-dimensional model for turbulent flow, combustion, and radiant heat transfer in a glass furnace. Some results from a high-temperature gas-fired glass furnace are also given.

Three-Dimensional Combustion Modeling in Municipal Solid-Waste Incinerator, K. S. Chen, Y. J. Tsai, and J. C. Lou, Journal of Environmental Engineering, pp. 166-174, February 1999.

This paper presents a three-dimensional model of the combustion process in a municipal solid-waste incinerator using finite-element analysis. Experimental measurements are compared with model predictions.

Direct-Fired Melter Performance Improved by Gas/Oxygen Firing, L. Kirk Klingensmith, pp. 14-18, Glass Industry, March 1986.

This article discusses the performance advantages of gas/oxygen combustion over plain gas combustion. By using a gas/oxygen mix furnace, natural gas consumption goes down and savings go up. Corning uses this technique in their production furnaces.

Hanford Waste Vitrification Plant Hydrogen Generation Study: Formation of Ammonia from Nitrate and Nitrate in Hydrogen Generating Systems, R. B King and N. K. Bhattacharyya, PNNL-10983, February 1996.

This report discusses the noble metal catalyzed formic acid reduction of nitrite and nitrate to ammonia during melter feed preparation for the Hanford Waste Vitrification Plant. This ammonia production coupled with hydrogen generation could lead to an explosion hazard in the plant off-gas system. The report may be useful for DWPF melter feed preparation and planning.

Small-Scale High Temperature Melter-1 (SSHTM-1) Data Package, G. L. Smith et al, PNNL-10993, February 1996.

The report discusses two melter feed batch experiments performed to examine various processing options and concerns, including hydrogen and ammonia generation as well as maintaining melt production rate. The data may be useful for DWPF melter feed preparation or the SRAT/SME operations.

Small-Scale High Temperature Melter-1 (SSHTM-1) Data Package: Appendix A, G. L. Smith et al, PNNL-10993, February 1996.

This document is an extension of the previous report and contains the nitric-only acid melter feed preparation data. There is detailed off-gas and redox information in this appendix. The data may be useful for DWPF melter feed preparation.

Small-Scale High Temperature Melter-1 (SSHTM-1) Data Package: Appendix B, G. L. Smith et al, PNNL-10993, February 1996.

This document is an another appendix of the SSHTM report and contains the glycolic acid melter feed preparation data. It contains detailed off-gas and redox information. The data may be useful for DWPF melter feed operations.

Noble Metal-Catalyzed Homogenous and Heterogeneous Processes in Treating Simulated Nuclear Waste Media with Formic Acid, R. B. King, N. K. Bhattacharyya, H. D. Smith, and K. D. Wiemers, Journal of Molecular Catalysis A: Chemical, vol. 107, pp. 145-152, 1996.

This article discusses the formic acid reactions catalyzed by Ru, Rh, and Pd that are part of treating typical nuclear waste for vitrification. In particular, the decomposition of formic acid to hydrogen and the generation of ammonia from formic reduction of nitrate and/or nitrite are examined. The data may be useful for DWPF melter feed preparation.

A Summary Report on Feed Preparation Offgas and Glass Redox Data for Hanford Waste Vitrification Plant: Letter Report, M. D. Merz, PNNL-11039, March 1996.

This report compares various feed preparation tests made for Hanford Waste Vitrification Plant (HWVP) by many different groups. Off-gas design data as well as melter feed preparation data are included. This data may be useful to DWPF melter feed operations.

Evaluation of High-Level Waste Vitrification Feed Preparation Chemistry for NCAW Simulant, FY 1994: Alternate Flowsheets (DRAFT) , H. D. Smith, M. D. Merz, K. D. Wiemers, G. L. Smith, PNNL-10992, February 1996.

This report evaluates several tests performed during fiscal years 1993 and 1994 to examine the effects of using reductants other than formic acid in the treatment of high level radioactive waste. Off-gas composition and generation are studied as well as waste slurry chemistry. The information may be applicable to DWPF SRAT/SME runs or melter feed preparation.

Hanford Waste Vitrification Plant Capacity Increase Options, D. E. Larson, PNNL-11095, April 1996.

This report discusses changes that would be necessary to the Hanford Waste Vitrification Plant (HWVP) to increase waste processing capability. One of the recommendations was to increase the melter feed waste loading or concentration. The information may be useful when evaluating larger SRAT/SME batches in DWPF.

Vitrification Development and Experiences at Fernald, Ohio, R. F. Gimpel, D. Paine, J. L. Roberts, N. Akgunduz, Institute of Nuclear Materials Management, 39th Annual Meeting, Naples Florida, July 26-30, 1998.

This paper looks at a seven month campaign for a one-ton per day Vitrification Pilot Plant (VITPP) at Fernald for processing radium and radon silo wastes. It mainly centers on the foaming problems encountered and the failure of the melter. The information may be useful to general DWPF melter operations.

Redox Reaction and Foaming in Nuclear Waste Glass Melting, J. L. Ryan, PNL-10510, August 1995.

This report reviews various studies on nuclear waste glass foaming and how redox affects foaming. In particular, the use of formic acid as a reductant is examined. The information may be useful for foaming and redox concerns in DWPF.

NCAW Feed Chemistry :Effect of Starting Chemistry on Melter Off-Gas and Iron Redox, P. A. Smith, J. D. Vienna, and M. D. Merz, PNL-10517, March 1995.

This report examines the effect of feed chemistry on cold cap behavior in the vitrification of simulated Neutralized Current Acid Waste at Pacific Northwest Laboratory. Experimental results are presented concerning iron redox of the melter feed and alternate reductants other than formic acid. The data may be useful for DWPF foaming issues.

Noble Metal and Spinel Deposition on the Floor of the Joule-Heated Ceramic Melter, V. Jain, S. M. Barnes, T. K. Vethanayagam, and L. D. Pye, Journal of the American Ceramic Society, vol. 74, no. 7, pp.1559-1562, July 1991.

This article discusses the deposition of insoluble and crystallized species on the bottom of the Slurry-Fed Ceramic Melter (SFCM) at the West Valley Demonstration Project. One of the findings is that most of the noble metals remain in the glass and do not settle to the bottom of the melter. The information may be useful for DWPF melter operation.

Conclusions

Out of all the materials reviewed, no data was found that could help relax some of the conservatism in the DWPF melter off-gas model. Several articles were found with some melter off-gas data but due to scale or different operational constraints, the data was not useful. As evidenced by the material reviewed, general melt production does not deal with slurry or wet feed. For a normal melt production, the feed is dried or calcined before going into the melter. The same type of setup is also used for incineration. The feed to an incinerator goes through a feed preparation process where liquid and solid materials are separated.

DWPF could drop the minimum plenum vapor space temperature limit if there were some data to substantiate such a change. Unfortunately, due to DWPFs unique operation, finding such data may not be possible. However, experiments could be conducted in the mini-melter going into the Thermal Fluid labs to examine various options for maximizing melter production without violating operating constraints. For the DWPF melter off-gas model, experiments could be conducted where melter off-gas is monitored surges while tracking key melter properties such as hydrogen concentration and vapor space temperature. Other planned experiments looking at reducing the amount of moisture in the feed or altering melter feed chemistry could be performed to help refine the current melter off-gas model. If no pilot melter experiments are possible, outside experts or consultants in melter off-gas/combustion modeling could be brought in to help.

Acknowledgments

I would like to thank the SRTC library staff for their assistance in learning what sources were available for literature searches and how to perform library searches from within Shrine.