reduction of boiler stack particulate emissions and scrubber water ...

REDUCTION OF BOILER STACK PARTICULATE EMISSIONS 

AND SCRUBBER WATER FLOW USING LOW-SODIUM COAL 

BY: 

DONALD D. HILL 

ENGINEERlNG & MAINTENANCE MANAGER 

FORT MORGAN FACTORY 

WESTERN SUGAR COMPANY 

18317 HWY. 144, FORT MORGAN, CO., 80701 

AND 

PATRICIA R. FULLER-PRATT 

MANAGER OF ENVIRONMENTAL AFFAIRS 

WESTERN SUGAR COMPANY 

1700 BROADWAY, SUITE 1600, DENVER, CO., 80290 

ABSTRACT 

Two 1947 coal-fired stoker boilers, using a low-pressure mid-1970's design venturi scrubber, were 

able to demonstrate compliance at one-half the regulated limit and less than 0.1 Ib/MMBTU by 

converting to a low-sodium coal. The sodium content in coal impacts the particulate emissions and 

is the cause of higher particulate emissions and higher opacity. Analysis indicates that the sodium 

content must be less than 2.5 percent, or the ash to sodium ratio must be greater than 40, to be 

effective in reducing particulate emissions and opacity. The higher ash content provides sites to 

absorb or attach the sodium in the boiler without overloading the pollution control devices. The 

increased ash bed also insulates the grates and allows for better combustion efficiency. 

305

INTRODUCTION 

Voluntary compliance tests for particulate emissions were performed in October of 1995 at the 

Western Sugar Company's Fort Morgan sugar beet processing plant. 

The boilerhouse contains two Babcock & Wilcox stoker-fired boilers. The units were placed in 

service in 1947 and, except for a short time using natural gas, have used Detroit Stoker stokers as 

the coal-firing system. Each boiler has an American Standard Series 361 fly-ash collector and an 

in-house (Great Western Sugar Company) designed low-pressure venturi scrubber. Exhaust gas 

streams from each boiler are combined in a common stack which has a chevron-type mist 

eliminator. 

BOILER STACK TESTS - 22 OCTOBER 1995 

Normal intercampaign maintenance was performed on the boiler equipment and the Detroit Stoker 

field service representative "tuned" the boiler combustion system the week prior to the October 

1995 tests. The particulate emission limit is 0.14 Ib.lMMBTU. The first day's test results were 

under the limit (see Table 1). The second day the limit was exceeded twice and the average for the 

three compliance runs was 0.16 Ib.lMMBTU. The information was presented to the State of 

Colorado under the State's program of voluntary disclosure and a second test was scheduled as 

quickly as possible. Also, several boiler consultants were contacted to observe the compliance 

retest. 

TABLE 1 

OCTOBER STACK TESTS 

PARTICULATE EMISSIONS 

OCTOBER 2 AND 3; 1995 

ITEM RUNNO.1 RUNNO.2 RUN NO.3 AVERAGE 

Boiler No.1 

PLUG 

CONE 

250 gpm 

285 gpm 

250 gpm 

280 gpm 

250 gpm 

280 gpm 

250 gpm 

282 gpm 

Boiler No.2 

PLUG 

CONE 

280 gpm 

260 gpm 

275 gpm 

250 gpm 

275 gpm 

250 gpm 

277 gpm 

253 gpm 

PARTICULATE 

EMISSIONS 

(lb.lMMBTU) 

0.128 

0.189 

0.163 

0.160 

306 

- - .... - -

RETESTS - 15 NOVEMBER 1995 

The coal supplier provided a consultant to review the coal as-delivered and as-fired, and also to 

observe the boiler operation. Detroit Stoker provided the same technician who was on site in 

October to "tune" the boilers. He also observed the boiler operation during the tests in order to 

advise us if any mechanical problems may have developed. A scrubber manufacturer was contacted 

to observe the venturi scrubber operation during the tests and to inspect it prior to the tests. This 

individual had been previously employed as a "stack tester" and also observed the stack testing 

company during the compliance runs. 

The November tests were run with more scrubber water flow, higher pressure drops across the 

scrubber, but no "hands-on" operation by any of the consultants. The average of the three 

compliance runs for particulates was 0.271 Ib.lMMBTU (see Table 2), which is nearly twice the 

permitted limit. 

TABLE 2 

NOVEMBER STACK TESTS 

P ARTICULATE EMISSIONS 

NOVEMBER 15 AND 16, 1995 

ITEM RUN NO.] RUN NO. 2 RUN NO.3 AVERAGE 

Boiler No.1 

PLUG 335 gpm 334 gpm 333 gpm 334 gpm 

CONE 340 gpm 338 gpm 337 gpm 338 gpm 

Boiler No.2 



PARTICULATE 

EMISSIONS 

(lb. / MMBTU) 0.269 0.280 0.265 0.271 

SODIUM 

EMISSIONS 

(lb. / MMBTU) 0.110 0.123 0.122 0.118 

SODIUM OXIDE 

(% in ASH) 8.015 6.685 8.05 7.58 

During the tests, the opacity of the stack was observed (not using Method 9) by all the consultants 

and a "blue haze" was evident after the vapor break of the "plume". The coal consultant suggested 

that the "blue haze" might be due to sodium and was a condition he had observed before with 

Northern Powder River Basin coal. The scrubber consultant agreed that this was possible, and 

307

suggested that a sub-micron sodium fume would pass through a low-pressure venturi scrubber. He 

suggested that we analyze the particulate catch for "sodium". This analysis by the stack testing 

company averaged 0.118 lb. Sodium/MMBTU, which is nearly 90% of the permitted limit. An 

analysis of the coal as-fired for sodium oxide, averaged 7.58% sodium oxide in the ash. When the 

coal shipments were reviewed for the 1995-1996 campaign (see Table 3), the percent sodium in the 

ash during the October test was around 4.0% and the highest values -- 7.0% to 8.0% -- occurred 

during the November test. The consultants agreed that the boilers were performing correctly and 

that the coal was the biggest contributor to the problem. 

TABLE 3 

COAL SIDPMENT DATA FOR 1995-1996 CAMPAIGN 

Date of lb/MMBTU % Ash % Sodium Calculated % Sulfur 

Shipment 

Ratio 

9/17/95 9,309 4.37 4.5 22.22 0.33 

9/24/95 9421 4.55 4.95 20.2 0.41 

9/29/95 9379 4.58 4.5 22.22 0.34 

10/3/95 9427 3.97 4.21 23.75 0.37 

10/4/95 9356 4.29 4.45 22.47 0.35 

10/11 /95 9438 3.79 5.32 18.8 0.35 

10113/95 9467 3.85 4.41 22.68 0.34 

10118/95 9244 4.5 3.91 25.58 0.33 

10/22/95 9553 3.98 5.19 19.27 0.3 

10/28/95 9407 3.82 4.42 22.62 0.34 

10/30/95 9368 4.13 6.74 14.84 0.3 

10/30/95 9377 4.71 6.44 15.53 0.36 

1114/95 9420 4.15 7.07 14.14 0.35 

11111195 9475 3.74 7.89 12.67 0.32 

11116/95 9453 3.96 8.35 1l.98 0.34 

11119/95 9612 4.42 5.19 19.27 0.33 

11122/95 9485 4.08 5.83 17.15 0.34 

11127/95 9328 4.47 4.62 2l.64 0.34 

12/2/95 9383 4.07 5.02 19.92 0.3 

12/7/95 9463 4.46 5.63 17.76 0.45 

12111/95 9222 4.37 6.57 15.22 0.33 

12114/95 9424 3.81 7.38 13.55 0.33 

12117/95 8795 4.6 1.47 68.03 0.15 

12/22/95 9442 3.6 5.26 19.01 0.32 

12/26/95 9434 3.94 5.09 19.65 0.35 

AVERAGES 9387 4.17 5.38 20.81 0.33 

308 

_ .-._---_..- .-... - -

ENGINEERING TESTS - 21 DECEMBER 1995 

A source for ]ow-sodium coal was found in the Southern Powder River Basin and a test burn and 

compliance test were arranged for December 21, 1995. These tests were not full compliance tests 

but were engineering-level tests only meant to test the "sodium in the coal" theory. Also, these tests 

were observed by a representative of the Colorado Department of PubEc Health and Environment, 

as were the November tests. However, no consultants were present. The scrubber water flows were 

returned to the levels of the October test (see Table 4) and the particulate emissions were an average 

of 0.09 IbIMMBTU, which is ]ess than 65% of the permit limit of 0.14 Ib.lMMBTU. Unfortunately, 

we were ten days away from the end of campaign and a full compliance test could not be scheduled 

until the start of the 1996 -1997 campaign. 

TABLE 4 

DECEMBER STACK TESTS ("ENGINEERING TESTS") 

PARTICULATE EMISSIONS 

DECEMBER 21, 1995 

ITEM RUN NO.1 RUN NO.2 AVERAGE 

Boiler No.1 

PLUG 200 gpm 200 gpm 200 gpm 

CONE 200 gpm 200 gpm 200 gpm 

Boiler No.2 

PLUG 195 gpm 200 gpm 198 gpm 

CONE 200 gpm 200 gpm 200 gpm 

PARTICULATE 

EMISSION S 

(lb.lMMBTU) 0.087 0.085 0.09 

CALCULATION MISCONCEPTION 

Research at another Western Sugar factory regarding opacity suggested that an Ash to Sodium-inthe-Ash 

ratio of 48 or better at that factory would produce an opacity of about 10%. The consultant 

suggested a b ~ end of "high" and "low" sodium coals to reduce opacity at that factory. However, 

that consultant felt that sodium wou1d not contribute much to particulate emissions (which proved 

incorrect in our testing at Ft. Morgan). 

The consultant's report attempted to establish the Ash/Sodium ratio by using lb. AshlMMBTU and 

lb. Sodium/MMBTU. Basically, this is mathematically incorrect. In order to calculate each of these 

numbers and then take the ratio you have essentially canceled out the units and the ratio is really 

one (1) divided by the Sodium in the Ash percentage expressed as a number, i.e. 2.5% Sodium in 

the Ash is equal to 0.025. Therefore, 1/0.025 = 40. For the Ft. Morgan factory, we developed a 

309

conservative estimate that a coal with an Ash to Sodium in the Ash ratio of greater than 40, or a 

Sodium in the Ash content of less than 2.5 %, would achieve compliance. 

COMPLIANCE AND ENGINEERING TESTS - 22 OCTOBER 1996 

A low-sodium Southern Powder Ri ver Basin coal was contracted for the 1996-1997 beet campaign. 

A compliance test was conducted on October 22, 1996 (see Tabl 5). The results averaged 0.072 

Ib.lMMBTU, which is well below the 0.14 Ib.lMMBTU particulate emission limit. 

TABLES 

OCTOBER 1996 COMPLIANCE DEMONSTRATION STACK TEST 

PARTICULATE EMISSIONS 

OCTOBER 22,1996 

ITEM RUN NO.1 RUN NO.2 RUN NO.3 AVERAGE 

Boiler No.1 



Scrubber Diff. Press. 5.8 in. H 2 O 5.6 in H 2 O 5.9 in H 2 O 5.8 in H 2 O 

Boiler No.2 



Scrubber Diff. Press 5.6 in. H 2 O 5.6 in H 2 O 5.6 in H 2 O 5.6 in H 2 O 

PARTICULATE 

EMISSIONS 

(lb.lMMBTU) 0.079 0.066 0.070 0.072 

After the compliance tests were completed, the water flows to the scrubber plug and cone and the 

venturi plug placement were varied in order to establish parameters which could be tested in order 

to prove compliance using parmetric monitoring for the Title V Operating Permit. A total of eight 

engineering tests were performed at four different water flows and lor pressure differentials (two 

tests at each level). 

~ 

The water flowrates for the plug and cone of the venturi were varied from 200 gpm to 150 gpm to 

100 gpm and the pressure drop was changed from 5.0, 4.0, to 3.0 in. H 2 0. The idea was to vary the 

water flow and hold the pressure drop constant to simulate a condition of loss/reduction of water 

flow (pump belt slippage, pat1ial blockage or some other reason). The pressure drop was varied 

while holding the water flow constant in order to simulate a loss in air flow (a mechanical problem 

with the fans or their steam-turbine drivers, a damper problem or some other reason). The 

variations all worked, except the 3.0 in. H 2 0 pressure drop setting, which required decreasing the 

water flow by 50 gpm in order to get the pressure to drop even though the venturi plug had been 

lowered to its lowest point. As the results show (see Table 6), the water flow variation tests had 

310

particulate emissions of 0.072, 0.076 and 0.078 lb.lMMBTU and the pressure drop particulate 

emission rates were 0.072, 0.09 and 0.088 lb.lMMBTU. 

TABLE 6 

OCTOBER 1996 "ENGINEERING" STACK TEST 

PARTICULATE EMISSIONS VARYING WATER IiLOW & PRESSURE DIFFERENTIAL 

OCTOBER 23 & 24, 1996 

VARYING WATER FLOW 

VARYING PRESSURE 

ITEM RUN NO.1 RUN NO.2 RUN NO.3 RUN NO.4 

Scrubber Water Flow 

PLUG & CONE #1 307 gpm 214 gpm 414 gpm 300 gpm * 

PLUG & CONE #2 309 gpm 211 gpm 412 gpm 296 gpm * 

Scrubber Differential Pressure 

BOILER N O. 1 5.5 in. H 2 0 4.9 in H 2 0 4.4 in H 2 0 3.4 in H 2 0 

BOILER N O. 2 5.3 in. H 2 0 5.0 in H 2 0 4.1 in H 2 0 3.3 in H 2 0 

Particulate Emissions 

(lb.lMMBTU) 0.079 0.066 0.070 0.072 

These engineering tests showed that there is a wide operating window for the scrubbers when using 

a low-sodium coal. It appears that low water flowrate and a small pressure drop will still allow the 

boilers to operate below their particulate permit limit of 0.14 Ib.lMMBTU. 

CONCLUSIONS AND BENEFITS 

The Fort Morgan factory is in compliance with boiler particulate limits when it uses low-sodium 

coal. The Fort Morgan factory can successfully demonstrate on-going compliance by monitoring 

the following parameters: 

• COAL SUPPLY 

Maintain a record of the coal analysis of each shipment of coal to the factory and verify 

that it is less than 2.5% Sodium in the Ash. (Ash/Sodium ratio of greater than 40). 

• SCRUBBER WATER FLOW 

Keep the water flow to each venturi plug above 100 gpm and 100 gpm to each venturi 

cone. These are recorded continuously on a strip chart recorder. 

311

• SCRUBBER PRESSURE DIFFERENTIAL 

Set the venturi plug at a point to maintain at least 2.5 in. H 2 

0 or more of pressure drop for 

each venturi scrubber. The pressure drops are also continuously recorded on strip chart 

recorders in the boiler control room. 

BENEFITS 

1. The original scrubber water flowrates had a "design" need for 800 gpm for each scrubber 

system or 1600 gpm for both, which all ended up in the ash pond. This flow has now 

been reduced to 200 gpm to 250 gpm for each system or 400 gpm to 500 gpm, a total 

savings of 1100 + gpm. 

2. By having a thicker ash bed, the combustion air entry points can be redirected to have 

the undergrate air decreased as the grates are better insulated and the overfire air 

increased to "lower" the flame and improve 02 addition in the suspended- burning zone. 

3. With better air flow distribution, even though the BTU content of the low-sodium coal is 

less than that of the previous higher-sodium coal, the combustion efficiency has 

improved and coal consumption is less (about 30 + tons per day). 

4. Post campaign boiler cleanup is easier and quicker, as the lower sodium coal does not 

"slag" as much and the slag that does form appears softer and easier to remove. 

312

reduction of boiler stack particulate emissions and scrubber water ...

Create successful ePaper yourself

Delete template?

Save as template?