Wisconsin Administrative Code
Department of Natural Resources
NR 400-499 - Environmental Protection - Air Pollution Control
Chapter NR 440 - Standards of performance for new stationary sources
Subchapter II - Standards of Performance
Section NR 440.684 - Onshore natural gas processing: SO2 emissions

1. "Acid gas" means a gas stream of hydrogen sulfide (H2S) and carbon dioxide (CO2) that has been separated from sour natural gas by a sweetening unit.

2. "Natural gas" means a naturally occurring mixture of a hydrocarbon and nonhydrocarbon gases found in geologic formations beneath the earth's surface. The principal hydrocarbon constituent is methane.

3. "Onshore" means all facilities except those that are located in the territorial seas or on the outercontinental shelf.

4. "Reduced sulfur compounds" means hydrogen sulfide (H2S), carbonyl sulfide (COS), and carbon disulfide (CS2).

5. "Sulfur production rate" means the rate of liquid sulfur accumulation from the sulfur recovery unit.

6. "Sulfur recovery unit" means a process device that recovers element sulfur from acid gas.

7. "Sweetening unit" means a process device that separates the H2S and CO2 contents from the sour natural gas stream.

8. "Total SO2 equivalents" means the sum of volumetric or mass concentrations of the sulfur compounds obtained by adding the quantity existing as SO2 to the quantity of SO2 that would be obtained if all reduced sulfur compounds were converted to SO2, ppmv or kg/dscm (lb/dscf).

1. "E" is the sulfur emission rate expressed as elemental sulfur in kg/hr (lb/hr), rounded to one decimal place.

2. "R" is the sulfur emission reduction efficiency achieved in percent carried to one decimal place.

3. "S" is the sulfur production rate in kg/hr (lb/hr), rounded to one decimal place.

4. "X" is the sulfur feed rate from the sweetening unit, that is, the H2S in the acid gas, expressed as sulfur, Mg/d (long ton/day), rounded to one decimal place.

5. "Y" is the sulfur content of the acid gas from the sweetening unit, expressed as mole percent H2S (dry basis) rounded to one decimal place.

6. "Z" is the minimum required sulfur dioxide (SO2) emission reduction efficiency, expressed as percent carried to one decimal place. Zi refers to the reduction efficiency required at the initial performance test. Zc refers to the reduction efficiency required on a continual basis after compliance with Zi has been demonstrated.

1. To determine compliance with the standards for sulfur dioxide specified in sub. (3) (a), during the initial performance test as required by s. NR 440.08, the minimum required sulfur dioxide emissions reduction efficiency (Z) is compared to the emission reduction efficiency (R) achieved by the sulfur recovery technology.

2. Following the initial determination of compliance as required by s. NR 440.08, any subsequent compliance determinations that may be required by the department shall compare R to Zc.

1. The average sulfur feed rate (X) shall be computed as follows:

X = K Qa Y

where:

X is the average sulfur feed rate, Mg/d (long ton/day)

Qa is the average volumetric flow rate of acid gas from sweetening unit, dscm/day (dscf/day)

Y is the average H2S concentration in acid gas feed from sweetening unit, percent by volume, expressed as a decimal

K is (32kg S/kg-mole)/((24.04 dscm/kg-mole)(1000kg S/Mg)) = 1.331 x 10-3 Mg/dscm for metric units, and is (32 lb S/lb-mole)/((385.36 dscf/lb-mole)(2240 lb S/long ton)) = 3.707 x 10-5 long ton/dscf for English units

2. The continuous readings from the process flowmeter shall be used to determine the average volumetric flow rate (Qa) in dscm/day (dscf/day) of the acid gas from the sweetening unit for each run.

3. The Tutwiler procedure in sub. (9) or a chromatographic procedure following ASTM E260-96, incorporated by reference in s. NR 440.17(2) (a) 75., shall be used to determine the H2S concentration in the acid gas feed from the sweetening unit. At least one sample per hour, at equally spaced intervals, shall be taken during each 4-hour run. The arithmetic mean of all samples shall be the average H2S concentration (Y) on a dry basis for the run. By multiplying the result from the Tutwiler procedure by 1.62 10-3, the units gr/100 scf are converted to volume percent.

4. Using the information from par. (b) 1. and 3., Tables 1 and 2 shall be used to determine the required initial (Zi) and continuous (Zc) reduction efficiencies of SO2 emissions.

1. The emission reduction efficiency (R) achieved by the sulfur recovery technology shall be computed for each run using the following equation:

R = (100 S)/(S + E)

2. The level indicators or manual soundings shall be used to measure the liquid sulfur accumulation rate in the product storage tanks. Readings taken at the beginning and end of each run, the tank geometry, sulfur density at the storage temperature and sample duration shall be used to determine the sulfur production rate (S) in kg/hr (lb/hr) for each run.

3. The emission rate of sulfur shall be computed for each run as follows:

E = Ce Qsd/ K1

where:

E is the emission rate of sulfur per run, kg/hr (lb/hr)

Ce is the concentration of sulfur equivalent (SO2 + reduced sulfur), g/dscm (lb/dscf)

Qsd is the volumetric flow rate of effluent gas, dscm/hr (dscf/hr)

K1 is a conversion factor, 1000 g/kg (7000 gr/lb)

4. The concentration (Ce) of sulfur equivalent shall be the sum of the SO2 and TRS concentrations, after being converted to sulfur equivalents. For each run and each of the test methods specified in this paragraph, the sampling time shall be at least 4 hours. Method 1 shall be used to select the sampling site. The sampling point in the duct shall be at the centroid of the cross- section if the area is less than 5 m2 (54 ft2) or at a point no closer to the walls than 1 m (39 in.) if the cross-sectional area is 5 m2 (54 ft2) or more and the centroid is more than 1 m (39 in.) from the wall.

1. The accumulation of sulfur product over each 24-hour period: The monitoring method may incorporate the use of an instrument to measure and record the liquid sulfur production rate, or may be a procedure for measuring and recording the sulfur liquid levels in the storage tanks with a level indicator or by manual soundings with subsequent calculation of the sulfur production rate based on the tank geometry, stored sulfur density, and elapsed time between readings. The method shall be designed to be accurate with " 2% of the 24-hour sulfur accumulation.

2. The H2S concentration in the acid gas from the sweetening unit for each 24-hour period: At least one sample per 24-hour period shall be collected and analyzed using the method specified in sub. (5) (b) 3. The department may require the owner or operator to demonstrate that the H2S concentration obtained from one or more samples over a 24-hour period is within " 20% of the average of 12 samples collected at equally spaced intervals during the 24-hour period. In instances where the H2S concentration of a single sample is not within " 20% of the average of the 12 equally spaced samples, the department may require a more frequent sampling schedule.

3. The average acid gas flow rate from the sweetening unit: The owner or operator shall install and operate a monitoring device to continuously measure the flow rate of acid gas. The monitoring device reading shall be recorded at least once per hour during each 24-hour period. The average acid gas flow rate shall be computed from the individual readings.

4. The sulfur feed rate (X): For each 24-hour period, X shall be computed using the equation in sub. (5) (b) 1.

5. The required sulfur dioxide emission reduction efficiency for the 24-hour period. The sulfur feed rate and the H2S concentration in the acid gas for the 24-hour period as applicable, shall be used to determine the required efficiency in accordance with the provisions of sub. (3) (b).

1. A continuous monitoring system to measure the total sulfur emission rate (E) of SO2 in the gases discharged to the atmosphere. The SO2 emission rate shall be expressed in terms of equivalent sulfur mass flow rates kg/hr (lb/hr). The span of this monitoring system shall be set so that the equivalent emission limit of sub. (3) (b) will be between 30% and 70% of the measurement range of the instrument system.

2. Except as provided in subd. 3.: A monitoring device to measure the temperature of the gas leaving the combustion zone of the incinerator, if compliance with sub. (3) (a) is achieved through the use of an oxidation control system or a reduction control system followed by a continually operated incineration device. The monitoring device shall be certified by the manufacturer to be accurate to within " 1% of the temperature being measured. When performance tests are conducted under the provision of s. NR 440.08 to demonstrate compliance with the standards under sub. (3), the temperature of the gas leaving the incinerator combustion zone shall be determined using the monitoring device. If the volumetric ratio of sulfur dioxide to sulfur dioxide plus total reduced sulfur (expressed as SO2) in the gas leaving the incinerator is w 0.98, then temperature monitoring may be used to demonstrate that sulfur dioxide emission monitoring is sufficient to determine total sulfur emissions. At all times during the operation of the facility, the owner or operator shall maintain the average temperature of the gas leaving the combustion zone of the incinerator at or above the appropriate level determined during the most recent performance test to ensure the sulfur compound oxidation criteria are met. Operation at lower average temperatures may be considered by the department to be unacceptable operation and maintenance of the affected facility. The owner or operator may request that the minimum incinerator temperature be reestablished by conducting new performance tests under s. NR 440.08.

3. The owner or operator may, as an alternative to subd. 2., install, calibrate, maintain, and operate a continuous emission monitoring system for total reduced sulfur compounds as required in par. (d) in addition to a sulfur dioxide emission monitoring system. The sum of the equivalent sulfur mass emission rates from the 2 monitoring systems shall be used to compute the total sulfur emission rate (E).

1. Data obtained from the sulfur production rate monitoring device specified in par. (a) shall be used to determine S.

2. Data obtained from the sulfur emission rate monitoring systems specified in par. (b) or (c) shall be used to calculate a 24-hour average for the sulfur emission rate (E). The monitoring system shall provide at least one data point in each successive 15-minute interval. At least 2 data points shall be used to calculate each 1-hour average. A minimum of 18 1-hour averages shall be used to compute each 24-hour average. NR 440.684

1. Any 24-hour period (at consistent intervals) during which the average sulfur emission reduction efficiency (R) is less than the minimum required efficiency (Z).

2. For any affected facility electing to comply with the provisions of sub. (7) (b) 2., any 24-hour period during which the average temperature of the gases leaving the combustion zone of an incinerator is less than the appropriate operating temperatures determined during the most recent performance test in accordance with the provisions of sub. (7) (b) 2. Each 24-hour period shall consist of at least 96 temperature measurements equally spaced over the 24 hours.

1. Iodine stock solution, 0.1N. Weigh out 12.7 g of iodine and 20 to 25 g cp potassium iodide for each liter of solution. Dissolve the KI in as little water as necessary and then dissolve the iodine in the concentrated KI solution, make up to proper volume, and store in a glass-stoppered brown glass bottle.

2. Standard iodine solution, 1 ml " 0.001771 g I. Transfer 33.7 ml of the 0.1N stock solution into a 250 ml volumetric flask, add water to the mark and mix well. Then, for a 100 ml sample of gas, 1 ml of standard iodine solution is equivalent to 100 grains of H2S per cubic foot of gas.

Starch solution. Rub into a thin paste about one teaspoonful of wheat starch with a little water, pour it into about a pint of boiling water and stir. After it has cooled, decant off the clear solution. Make fresh solution every few days.