SOUTH COAST AIR QUALITY MANAGEMENT DISTRICT
RULE 1189 - EMISSIONS FROM HYDROGEN PLANT PROCESS VENTS
(Adopted January 21, 2000)
(a) Purpose and Applicability
The purpose of this rule is to reduce emissions of volatile organic compounds (VOCs) from hydrogen plant process vents. The rule applies to all hydrogen plants that produce any hydrogen for use in petroleum refining operations.
For the purpose of this rule, the following definitions shall apply:
(c) Requirements for Existing Hydrogen Plants
(d) Requirements for New or Reconstructed Hydrogen Plants
(e) Monitoring, Reporting and Recordkeeping Requirements
(f) Test Methods
The following test methods shall be used, as applicable, to determine compliance with this rule. All test methods referenced below shall be the most recent version issued by the respective organization. Alternative test methods may be used if they are determined to be equivalent and approved in writing by the Executive Officer, and by the California Air Resources Board and the U.S. Environmental Protection Agency.
Source Test Protocol for VOC Emissions from High Moisture
Hydrogen Plant Process Vents
This source test protocol provides guidance for determining the VOC emission rates from hydrogen plant process vents in terms of pounds of VOCs per million standard cubic feet of hydrogen produced (lb/MMscf). It specifies general conditions under which the source tests should be conducted in order for the Executive Officer to accept the test results as evidence for compliance demonstration with applicable provisions of Rule 1189. The SCAQMD Method 25.3 is the primary reference test method upon which this test protocol relies to determine the VOC and CO2 concentrations in various streams. Other standard methods such as SCAQMD Methods 1.1/2.1 and 5.1 are also used to determine flow rates and for collecting representative samples. The protocol establishes guidelines for appropriate use of these test methods on hydrogen plant process vents. Since some of the vent streams from the hydrogen plants are difficult or in some cases impossible to be tested by the reference methods, the protocol also establishes criteria under which the principles of mass balance (material balance) may be used instead.
DETERMINATION OF FLOW RATE
|Flow rates shall be determined by direct measurement except when direct measurement is infeasible and the Executive
Officer approves an alternative mass balance approach upon request. Direct flow rate measurement shall follow the
standard SCAQMD Method 1.1/2.1 Pitot tube traverse approach with sampling ports installed. Cyclonic flow checks
are required as part of each test. Installation of sampling ports, when possible, is recommended for purposes of
Where sample location or other constraints do not allow direct measurement of flow rates, the hydrogen plant operator shall submit a written request to the Executive Officer for approval of an alternative mass balance approach. The request shall include descriptions of the test constraints, the input to be used for calculating the flow rate and descriptions of the reliability of the input. Flow rates of CO2 vents can be calculated by a carbon mass balance on the process and feed material. Mass emissions by this approach would require measurements of VOC and CO2 at the CO2 vents utilizing SCAQMD Method 25.3 as described in this protocol. Flow rates must be determined and carbon and hydrogen stoichiometric analyses must be performed for all feed streams that enter the process.
Flow rates for the deaerator vents can be difficult to measure either directly or by mass balance. Direct measurement is impeded by the common use of silencers at the deaerator vents causing elevated pressures at sampling ports. When practicable, a stack extension shall be employed in these cases for sampling. Mass balances cannot be applied for calculating flow rate since the primarily steam effluent condenses to an unknown extent in the process. Therefore, upon approval by the Executive Officer, an alternative mass balance approach may be used to directly calculate VOC mass emissions from deaerator vents without determining the flow rate. This approach is described in the section Determination of Deaerator Emissions Using Mass Balance.
DETERMINATION OF GASEOUS VOC OR TOTAL VOC WHEN DROPLETS ARE NOT PRESENT
To determine the appropriate sampling method for the VOC emissions, a determination of whether or not droplets are present at the sampling location must be made. The absence of droplets is verified by a stack temperature above the dew point of the gases at the sampling location (higher temperature if under pressure). Alternatively, the absence of droplets can be verified by similar (within 10%) emissions as measured by both condensable methods of this protocol (Method 5.1 versus Method 25.3) as measured by previous testing.
Provided that it has been determined that droplets are not present at the sampling location, SCAQMD Method 25.3 as shown in Figure 1 must be used to measure the gaseous portion of the VOC, and/or the total VOC. For most cases, the CO2 vent can be sampled by using Method 25.3 since the temperature is expected to be above the dew point at the sampling location. For the primarily steam, deaerator exhaust, Method 25.3 must be supplemented by impinger sampling if the temperature is less than 212 oF.
For the deaerator vent, the trap volume specified in Method 25.3 must be increased to accommodate the high moisture. Using the six-liter canisters specified in Method 25.3, approximately 50 ml condensing water may be present. To accommodate for an initial 10 ml water charge and 1 ml of line rinse, a trap volume of 70 - 90 ml should be employed. For the CO2 vent, the trap volume specified in Method 25.3 may or may not need to be increased depending on the moisture present.
To accommodate for potentially high concentrations as compared to the 50 ppm range that Method 25.3 is intended, the calibration range of the analytical instrument can be extended and/or dilution techniques employed. This is acceptable to the applicability of Method 25.3 since the method allows its use for higher concentrations when primarily water soluble VOC are present, subject to SCAQMD approval.
In employing Method 25.3, condensation must not occur prior to the flexible Teflon connector hose as in Figure 1.
DETERMINATION OF CONDENSABLE VOC WHEN DROPLETS ARE PRESENT
|When droplets are present, a sample must be collected isokinetically using SCAQMD Method 5.1 (EPA Method 5) with
the filter omitted. This method is likely to be applied exclusively to the deaerator vent and only when the temperature
is less than 212 oF and the mass balance approach cannot be applied. The allowable range of isokinetics
can be extended to 110% or less due to difficulties in maintaining isokinetics with the high moisture causing isokinetics
of much less than 100%. The condensable VOC is expected to consist primarily of water-soluble methanol. For purposes
of this protocol only, it can be assumed that the minimum 30 cubic feet of required sampling volume can be satisfied
by applying the wet volume collected with an added safety margin. A minimum wet volume of 60 actual cubic feet
and a minimum dry volume of 1.5 dry cubic feet are therefore required. These are similar to the volumes collected
in previous development work. This wet sample volume is subject to the additional requirement that the analysis
yields results of greater than five times the lower detection limit. The sampling rate is, therefore, much lower
than is normally seen at the meter. The nozzle is sized so that the specified sample volume is collected over an
approximate 60 minute period or less if the last non-silica gel impinger becomes full during the sampling. For
sampling periods of less than 60 minutes, triplicate sampling is required.
Method 5.1 has provisions for including additional or larger volume impingers for high moisture sources. For 100 cubic feet of wet sample, this equates 2000 ml or more of condensate, which is capable of filling several standard impingers. The additional impinger approach is preferred over the enlarged impinger approach due to difficulties associated with poor heat-transfer surface area. The front impingers have been observed to experience overflow difficulties due to higher gas velocities in the front section. For these reasons a precondenser is highly recommended. The recommended configuration is a precondenser followed by five empty impingers followed by the standard Method 5.1 train without a filter as shown in Figure 2.
After completion of the sampling, the sampling train must be tightly sealed and kept chilled by ice or kept at 32 oF - 45 oF until analysis and during recovery. The sampling train is weighed then recovered and mixed into two composites (back and front sections) of the impinger contents using a minimal amount of rinse water. The back section consists of the last two impingers before the silica gel. The front section consists of the remaining non-silica gel impingers and probe and line rinses. During the recovery, sample agitation must be kept at a minimum to avoid loss of the volatile components. The samples must be analyzed within 72 hours of collection. The front section and back section composites are weighed and analyzed separately for VOC by the condensate trap analysis of SCAQMD Method 25.3. The stack concentration and mass emissions are calculated as in the Calculation section.
DETERMINATION OF DEAERATOR EMISSIONS USING MASS BALANCE
|The mass balance approach for calculating deaerator mass emissions must only be used when safety constraints dictate that direct measurement should not be performed. Since past experiences with the mass balance approach have yielded high variability, a minimum of eight runs are required. Each run shall consist of collecting process samples and flow rate data for all streams that enter and exit the deaerator including the steam (condensate). The samples must be collected in an inert container such as glass with Teflon lined lids with zero headspace. The samples must be kept chilled until analysis and analyzed within 72 hour of collection for ppm VOC as carbon by weight by the condensate trap analysis in SCAQMD Method 25.3. Process flow rates must be obtained using calibrated instruments. Additionally, aside from the VOC emissions rate, the deaerator vent rate must be calculated as the difference between total inlet and outlet flows for quality assurance. A negative value, a high positive value, or large deviation between runs may be an indicator of an error and may cause the Executive Officer to reject the test results.|
CO2 Vent Flow Rate - Material Balance Alternative. If the CO2 vent flow rate is determined by the carbon material balance, the flow rate shall be determined by the following relationship:
QCO2 = QCin - QCout Equation 1
QCO2 = CO2 vent flow rate (dscfm) QCin = Flow rate into the unit on a carbon basis (dscfm) based on the feed rates or the average hydrogen production rate and a stoichiometric analysis of carbon and hydrogen in the process feed during testing. QCout = Flow rate out of the unit on a carbon basis for streams containing carbon such as with the hydrogen product stream.
Condensable VOC when Droplets are Present. If droplets are present and the Method 5.1 sampling was employed, the concentration of condensable VOC is determined for both front and back sections of each sample using the following equation in Method 25.3 Section 4.7 with the variables redefined as follows:
Cw = (Ci x Vi x Vid)/(Vc x Ac) Equation 2
Ac = Atomic weight of carbon (12.01 g/mol) Cw = gaseous concentration of TOC as ppmC in condensate trap water Ci = TOC concentration in ug/ml of condensate trap water (Assume TOC concentration ug/g = ug/ml at 4oC) Vi = volume collected in all impingers excluding the silica gel in ml Vid = volume of ideal gas per mole (gram mole) at 60 oF (0.836 scf/mol) Vc = metered gas volume in dry standard cubic feet
If the back section concentration is more than 10% of the front section concentration, then the sampling must be invalidated and re-run with more cooling in the front section.
VOC Concentration. If droplets were present, as verified by stack temperature or previous testing, the VOC concentration (ppmC) is reported as the sum of both sections of the VOC analysis of the Method 5.1 train, and the canister portion of the Method 25.3 analysis in units of ppmC. If no droplets were present, the ppm VOC is reported as the sum of the Method 25.3 trap and canister analysis as ppmC. The following relationship is used generically for both cases for each process vent:
C = Ccond + Cgas Equation 3
C = VOC concentration (ppmC by volume) Ccond = Concentration of condensable VOC by both sections of Method 5.1 if
droplets present or by Method 25.3 if no droplets present (ppmC by volume)
Cgas = Concentration of gaseous VOC by Method 25.3 (ppmC by volume)
VOC Mass Emissions. Mass emissions from each stack are calculated using the concentration in Equation 3 in ppmC by volume, the dry standard volumetric flow rate from each stack, and the molecular weight and carbon number of methanol (MW = 32 lb/lb-mol, C# = 1) as follows:
M = F x C x (MW/C#) x Q Equation 4
F = 1.583 x 10-7 (Conversion factor in min-lb-mol/hr-scf-ppm) M = VOC mass emissions (lb/hr) C = VOC concentration (ppmC as volume) MW/C# =32 lb/lb/mol Q = Flow rate (dscfm)
Alternative VOC Mass Emissions for Deaerator. When the mass balance approach is used, the emissions from the deaerator vent may be calculated using process flow rates and Method 25.3 analyses of process samples using the following equation:
M = S ( Qin x Cin x Fmw / 106) - S ( Qout x Cout x Fmw / 106) Equation 5
M = VOC mass emissions (lb/hr) Qin = Inlet Process Flow Rates (lb/hr) Cin = VOC concentration in inlet process streams by Method 25.3 (ppmw) Fmw = Molecular weight correction = (32 lb/lb-mole) / (12 lb/lb-mole) = 2.67 Qout = Outlet Process Flow Rates (lb/hr) Cout = VOC concentration in outlet process streams by Method 25.3 (ppmw)
Total VOC Mass Emissions. Total VOC Mass Emissions in lb/hr is calculated by summing VOC Mass Emissions from all vent stacks using the following equation:
T = S M Equation 6
T = Total VOC Mass Emissions (lb/hr) M = VOC Mass Emissions from all individual vents stacks (lb/hr)
Total VOC Mass Emissions per Hydrogen Produced. Total VOC Mass Emissions in units of lb/MMscfhydrogen produced is calculated by using the following equation:
E = (2400 x T) / (P x H2) Equation 7
E = Emissions in lb/MMscfhydrogen produced T = Total VOC Mass Emissions (lb/hr P = Purity of hydrogen product stream (%) as determined by an approved method H2 = Average hydrogen production rate during testing (MMdscfm)
TEST REPORT REQUIREMENTS
The final Source Test Report must include the following information:
Figure 1- Sampling Equipment for Gaseous VOC or Total VOC
When Droplets are not Present
Figure 2- Sampling Equipment for Condensable VOC when Droplets are Presen