Measured and estimated benzene and volatile organic carbon (VOC) emissions at a major U.S. refinery/chemical plant: Comparison and prioritization

Figures & data

Table 1. Industrial areas targeted for DIAL measurements of alkane VOC and benzene emissions and their descriptions.

Industrial area	Description	Emissions measured
Aromatics Concentration Unit (ACU)	Distillation and extraction equipment for producing benzene, toluene, and xylenes from reformate and benzene concentrates.	Alkane VOC, benzene
Benzene Extraction Unit (BEU)	Distillation and extraction equipment for recovering benzene and toluene from benzene concentrate and for producing solvent-grade benzene and aromatic-free, high-naphtha-content raffinate.	Alkane VOC, benzene
Catalytic Reformer (CR)	Produces reformate from light naphtha, thereby increasing the octane rating.	Alkane VOC
Wastewater 1	Trickling filter, dissolved air floatation unit, and aeration basins for wastewater treatment.	Alkane VOC, benzene
Wastewater 2	Various tanks, clarifiers, and aeration basins for wastewater treatment.	Alkane VOC
Tank Set 1	Two internal floating roof tanks storing benzene column tops from the BEU.	Benzene
Tank Set 2	One internal floating roof tank storing benzene column tops from the BEU.	Benzene
Tank Set 3	Two internal floating roof tanks storing off-specification benzene.	Benzene
Tank Set 4	Two internal floating roof tanks storing pyrolysis gasoline (36% benzene by weight) and recovery oil (15% benzene by weight).	Benzene
Tank Set 5	Three external floating roof tanks storing Maya Crude Oil.	Alkane VOC
Tank Set 6	Two external floating roof tanks storing Maya Crude Oil.	Alkane VOC
Tank Set 7	Two internal floating roof tanks storing high-sulfur catalytic cracker feed.	Alkane VOC
Tank Set 8	Four fixed roof tanks—two storing distilling kerosene and two storing hydrocracker feed or gas oil.	Alkane VOC
Tank Set 9	Two external floating roof tanks storing Bonga Crude Oil.	Alkane VOC

Table 2. Summary statistics of measured benzene emissions by emission location (lb/hr).

	ACU/BEU	Wastewater	Tank	Tank	Tank	Tank	Tank
Emission location	process	process 1	Set 1	Set 2	Set 3	Sets 1, 2, 3	Set 4
n	22	20	3	6	8	17	58
Number of days	2	2	1	1	1	3	3
Minimum	3.16	2.55	19.80	2.68	–7.51	–7.51	0.06
Maximum	23.65	10.29	21.97	11.70	42.01	42.01	32.50
Mean	12.47	5.69	20.62	5.07	14.42	12.21	11.01
Median	12.04	5.04	20.09	3.78	11.54	10.05	6.06
SD	6.95	1.95	1.18	3.44	17.58	13.19	10.66
5%ile	4.60	3.68	19.83	2.69	–5.41	–2.71	0.19
25%ile (Q1)	5.56	4.46	19.95	2.92	0.72	2.71	2.58
50%ile (Q2)	12.04	5.04	20.09	3.78	11.54	10.05	6.06
75%ile (Q3)	17.51	6.74	21.03	5.31	26.23	20.09	21.52
95%ile	23.48	9.35	21.78	10.21	39.31	35.84	29.31
Distribution^a	Normal	Normal	NA	Gamma	Normal	Gamma	None
95th Percentile UCL of mean^a	15.02	6.44	NA	8.96	26.20	17.80	17.12

Notes: SD: standard deviation. NA: not enough data.

^aDistribution and 95th upper confidence limit of the mean calculated using EPA ProUCL version 4.1.

Figure 1. Wastewater 1 unit: (a) Contour plot of DIAL concentration profile. (b) Visualization of the flux measurement.

Figure 2. Tanks Set 4: (a) Contour plot of DIAL concentration profile. (b) Visualization of the flux measurement.

Table 3. Summary statistics of measured alkane VOC emissions by emission location (lb/hr).

	ACU/BEU		Wastewater	Wastewater	Tank	Tank	Tank	Tank	Tank
Emission location	process	CR	Process 1	Process 2	Set 5	Set 6	Set 7	Set 8	Set 9
n	16	22	34	18	19	9	8	23	11
Num of days	1	2	3	1	1	1	1	2	2
Min	4.69	2.10	1.76	16.17	9.89	6.18	32.62	17.74	9.48
Max	72.21	35.98	1420.00	32.38	29.82	14.71	68.52	42.61	23.24
Mean	58.18	18.04	503.10	25.35	17.97	10.90	48.41	32.43	15.88
Median	63.44	18.76	469.80	26.37	18.68	10.96	46.48	32.79	15.11
SD	17.71	11.48	430.80	4.92	5.54	3.62	14.50	7.04	4.49
5%ile	20.90	5.10	2.06	18.73	11.44	6.34	32.85	20.55	10.54
25%ile (Q1)	58.36	7.17	27.94	21.45	12.94	7.21	36.47	27.37	12.74
50%ile (Q2)	63.44	18.76	469.80	26.37	18.68	10.96	46.48	32.79	15.11
75%ile (Q3)	67.70	29.33	677.40	29.50	22.48	14.28	59.94	37.40	18.40
95%ile	70.62	34.82	1355.00	32.25	24.70	14.57	66.85	42.29	23.06
Distribution^a	None	Gamma	None	None	Normal	Normal	Normal	Normal	Normal
95th Percentile UCL of mean^a	77.48	23.89	964.60	27.37	20.18	13.15	58.12	34.95	18.34

Notes: SD: standard deviation.

^aDistribution and 95th upper confidence limit of the mean calculated using EPA ProUCL version 4.1.

Table 4. Comparison of benzene emission factor emission estimate and measured emissions of by emission location (lb/hr).

	ACU/BEU	Wastewater	Tank	Tank	Tank	Tank	Tank
Emission location	process	process 1	Set 1	Set 2	Set 3	Sets 1, 2, 3	Set 4
Mean	12.47	5.69	20.62	5.07	14.42	12.21	11.01
Median	12.04	5.04	20.09	3.78	11.54	10.05	6.06
Distribution^a	Normal	Normal	NA	Gamma	Normal	Gamma	None
95th Percentile UCL of mean^a	15.02	6.44	NA	8.96	26.20	17.80	17.12
Emission factor estimate^b	3.41	0.20	0.12	0.02	0.55	0.44	2.00
Ho: measured emission ≤ EF estimate	Reject (P < 0.0001)	Reject (P < 0.0001)	NA	Reject (P < 0.002)	Reject (P < 0.0001)	Reject (P < 0.0001)	Reject (P < 0.0001)
Multiplier^c	4.40	32.20	NA	448.00	47.64	40.45	8.56
Underestimation error	11.61	6.24	NA	8.94	25.65	17.36	15.12
Relative error (%)	77.30	96.89	NA	99.78	97.90	97.53	88.32

Notes: NA: not enough data.

^aDistribution and 95th percentile upper confidence limit of the mean calculated using EPA ProUCL version 4.1.

^bEstimate emission from emission factor.

^cMultiplier is 95th percentile upper confidence limit of the mean/estimate from emission factor.

Figure 3. Distribution of measured benzene emissions in relation to emission factor estimate (lb/hr).

Table 5. Comparison of alkane VOC emission factor emission estimate and measured emissions of by emission location (lb/hr).

Emission	ACU/BEU		Wastewater	Wastewater	Tank	Tank	Tank	Tank	Tank
location	process	CR	process 1	process 2	Set 5	Set 6	Set 7	Set 8	Set 9
Mean	58.18	18.04	503.10	25.35	17.97	10.90	48.41	32.43	15.88
Median	63.44	18.76	469.80	26.37	18.68	10.96	46.48	32.79	15.11
Distribution^a	None	Normal	None	None	Normal	Normal	Normal	Normal	Normal
95th Percentile UCL of mean^a	77.48	23.89	964.60	27.37	20.18	13.15	58.12	34.95	18.34
Emission factor estimate^b	2.50	20.70	11.00	5.90	2.20	0.60	0.40	1.12	0.40
Ho: Measured emission ≤ EF estimate	Reject (P < 0.0001)	Fail to Reject (P = 0.855)	Reject (P < 0.0001)	Reject (P < 0.0001)	Reject (P < 0.0001)	Reject (P < 0.0001)	Reject (P < 0.0001)	Reject (P < 0.0001)	Reject (P < 0.0001)
Multiplier^c	30.99	1.15	87.69	4.64	9.09	21.92	145.30	31.21	21.92
Underestimation error	74.98	3.19	953.60	21.47	17.80	12.55	57.72	33.83	17.94
Relative error	96.77	13.35	98.86	78.44	89.00	95.44	99.31	96.80	97.82

Notes: ^aDistribution and 95th percentile upper confidence limit of the mean calculated using EPA ProUCL version 4.1.

^bEstimate emission from emission factor.

^cMultiplier is 95th percentile upper confidence limit of the mean/estimate from emission factor.

Figure 4. Distribution of measured VOC emissions in relation to emission factor estimate (lb/hr).

Figure 5. VOC and benzene emissions: underestimation and relative error, magnitude of measured emissions, and revision prioritization.

Figure 6. Measured vs. emission inventory reported site emissions.