Electron Beam—Zapit Processing Unit

Current Status of Technology

Advanced Oxidation Technologies, Inc. owns patent of former Zapit Technology, Inc. Status being determined.

Description of Technology

Electron beam technology has been used for industrial applications for over 30 years. Zapit Technology, Inc. of Santa Clara, California, developed a gas phase VOC destruction system that is a non-burning, on-site, electron beam technology. In Zapit’s non-thermal oxidation process, a beam of electrons is passed through a thin window into a reaction chamber where the electrons react with the vapor stream to create free radicals that break down the complex organic molecules. Adjusting beam power, and the addition of oxidizing agents modifies the DRE of the e-beam. The system produces carbon dioxide, water and acid gases from halogenated hydrocarbons. These acids can be neutralized in a caustic scrubber.

The system consists of a prototype Zapit Processing Unit (ZPU), containing the following components:

· Sealed-tube electron beam generator and reaction chamber

· Sheet electron beam generator

· High-voltage power supply and control panel

· Multi-tray air stripper or desorber

· Packed-bed scrubber or adsorber

· Activated charcoal adsorbers for both liquid and gas phases

· On-line analyzers

· Blower

· Two 500-gallon polyethylene storage tanks

A simplified schematic of the system is shown in figure 1 below.

The reaction chamber is cylindrical and approximately 20 inches long and 8 inches in diameter, and constructed of stainless steel. A 13 inch by 2.5 inch window system along the top of the reactor allows electrons to pass from the electron source vacuum chamber into the vapor stream. Within the chamber the VOC stream is exposed to 0-20 mA of 170 keV electrons. Approximately 28% of the power provided by the e-beam source is transmitted into the reaction chamber. Zapit expects approximately 50% transmission efficiencies in commercial systems. Gas temperature, pressure, and composition are measured at the outlet of the ZPU reaction chamber.

The effluent from the reaction chamber are passed through a caustic scrubber containing continuously recirculating sodium hydroxide. The scrubber was designed to handle flows up to 500 cfm, however this demonstration had a nominal flow of 3 cfm. The scrubber effectively removed nitric acid, which can interfere with detection of NO_x by chemiluminescent NO_x analyzers. The effluent from the scrubber was passed through a vapor-phase carbon canister before being vented to the atmosphere.

Site and Contaminants Description

Bench scale tests of the electron beam technology were conducted to determine if this technology would be suitable for application at McClellan Air Force base. Under subcontract with Radian Corporation, the tests were conducted at Zapit Technology at the University of Tennessee’s Space Institute.

Previously Zapit Technologies demonstrated a bench scale system capable of achieving 98% DRE for an entire off gas stream from McClellan’s SVE. Samples of the off gas were placed in Tedlar bags and transported to Zapit’s test cell. As a result of this demonstration, McClellan recommended a performance test of a working, flow-through prototype before installing an e-beam pilot unit at McClellan. The flow-through prototype demonstration was designed in two phases. Phase I consisted of a bench scale steady-state test on two soil gas mixtures, while phase II would involve an on-site, pilot demonstration following phase I. Phase I failed to show viability of the technology pilot demonstration at McClellan. The results of the phase I bench scale test are presented here.

The simulated soil gas compositions are listed in table 1 below.

Table 1. Simulated Soil Gas Inlet Compositions for Zapit E-Beam Technology
Compound	Mix #1 Concentration (ppmv)	Mix #2 Concentration (ppmv)
1, l, 1-Trichloroethane (TCA)	8	1,657
1,1,2-Trichloroethane (TCA)	30	0
l,l-Dichloroethene (DCE)	15	1,018
1,1 -Dichloroethane (DCA)	0	66
1,2,4-Tnmethylbenzene	0	10
Acetone	15	0
Benzene	10	0
Chlorobenzene	0	4
Freon® 12	0	8
Freon® 113	150	88
Methylene chloride	0	50
Tetrachloroethene (PCE)	300	0
Toluene	70	45
Trichloroethene (TCE)	300	300
cis- 1,2-Dichloroethene (DCE)	200	62
m,p-Xylene	40	2
o-Xylene	95	5
Vinyl chloride	120	30

Performance of Technology and DRE

For each of the two gas mixtures, the optimum combination of beam power and promoter dose was calculated to maximize DRE of the VOCs while minimizing NO_x formation. Optimization tests were run at three different beam powers at zero promoter dose, and at three different promoter doses with beam power held constant. Since the scrubber was oversized the concentration of organic compounds in the scrubber liquid never achieved steady state, and no make-up caustic solution was required to maintain a high pH. The scrubber appeared to be absorbing organic compounds when the solution was fresh, and desorbing compounds from the liquid to the gas phase after periods where the scrubber received high levels of organic compounds. Therefore the DREs are calculated based on the effluent from the ZPU and not the scrubber. Important values for estimating E-beam process emissions are the NO_x, HCl, HF and HNO₃ concentrations exiting the scrubber.

Field Performance Data

Tables 2 and 3 below present the DREs for the e-beam technology bench scale demonstration of the two different soil gas mixtures.

Table 2. DREs of the electron beam bench scale technology demonstration for soil gas mixture 2.
Date:	3/29/95	3/29/95	3/29/95	3/30/95	3/30/95	4/6/95	4/7/95
Beam Dose (J/g)	134	268	535	535	507	535	535
Promotor Dose (g/min)	0	0	0	0.6	1.2	0	0
Organic Compound DRE(%)
1, l, 1-Trichloroethane	58.5	65.5	96.9	90.5	96.3	86.7	91.3
1,1-Dichloroethene	99.1	99.4	99.5	99.7	99.7	99.3	99.3
l,l-Dichloroethane	66.8	85.4	99.0	99.9	99.9	95.2	99.9
1,2,4-Tnmethylbenzene	98.3	96.5	63.0	98.6	97.9	ND	85.6
Chlorobenzene	20.8	52.0	91.6	98.1	98.1	95.1	96.5
Freon® 12	49.2	54.1	85.3	75.8	80.2	55.7	48
Freon® 113	88.9	71.2	86.3	78.2	81.5	71.8	78.1
Methylene chloride	77.0	87.8	97.9	96.8	97.3	95.3	96.9
Toluene	95.0	99.8	99.8	99.8	99.8	72.0	98.3
Trichloroethene	96.1	97.8	95.6	98.9	99.4	97.5	97.3
Cis-1,2-Dlchloroethene	99.9	99.9	99.4	99.9	99.9	99.8	99.8
m,p-Xylene	99.4	98.9	98.	76.9	97.3	96.5	95.1
o-Xylene	99.0	99.1	98.7	84.0	98.3	90.9	89.5

Vinyl chloride	99.9	99.8	9.8	99.96	99.8	99.8	99.6
Total	75.1	78.9	97.0	93.6	97.0	90.2	93.6
NOx (ppmv) ZPU outlet/ scrubber outlet	355/112	522/178	690/135	391/150	384/160	750/160	825/120
CO (ppmv) ZPU outlet/ scrubber outlet	1150/1120	1825/1720	1955/1955	1715/1685	1450/1370	1900/1800	1950/1890
HCl (ppmv) ZPU outlet/ scrubber outlet	NA/NA	NA/NA	NA/NA	NA/NA	NA/NA	1227/13	597/12
HF (ppmv) ZPU outlet/ scrubber outlet	NA/NA	NA/NA	NA/NA	NA/NA	NA/NA	2320/0.39	66/0.62
HNO3 (ppmv) ZPU outlet/ scrubber outlet	NA/NA	NA/NA	NA/NA	NA/NA	NA/NA	27/1.3	19/0.48
NA = Not available

Table 3. DREs of the electron beam bench scale technology demonstration for soil gas mixture 1.
Date:	3/6/95	3/6/95	3/6/95	3/10/95	3/10/95	3/15/95	4/12/95
Beam Dose (J/g)	54	134	535	134	125	294	321
Promotor Dose (g/min)	0	0	0	0.6	1.2	0	0
Organic Compound DRE(%)
1, l, 1-Trichloroethane (TCA)	26.0	48.1	69.2	51.6	89.1	74.4	66.0
1,1,2-Trlchloroethane (TCA)	54.0	72.0	95.9	71.4	94.3	90.9	75.3
l,l-Dichloroethene (DCE)	99.7	99.6	99.5	99.6	98.9	99.1	98.0
Acetone	47.9	81.1	95.6	71.2	55.3	58.3	75.1
Benzene	49.9	77.2	93.1	85.4	94.6	81.4	80.2
Freon® 113	27.9	52.7	93.2	50.7	91.2	75.6	68.7
Tetrachloroethene (PCE)	88.9	98.2	99.1	98.4	98.9	68.3	91.3
Toluene	90.2	99.6	99.7	99.3	99.8	95.5	79.5
Trichloroethene (TCE)	96.0	99.6	99.99	99.7	99.8	97.7	95.7
cis- 1,2-Dichloroethene (DCE)	96.1	99.9	99.9	99.96	99.7	99.1	96.7
m,p-Xylene	97.7	98.8	98.8	99.6	99.6	98.6	88.0
o-Xylene	99.1	99.5	99.5	99.7	99.3	90.0	83.0

Vinyl chloride	99.2	99.98	99.98	99.9	99.97	99.9	99.95
Total	81.2	90.5	98.2	90.1	97.7	84.8	88.0
NOx (ppmv) ZPU outlet/ scrubber outlet	40/NA	97/NA	394/NA	55/NA	200/NA	400/NA	560/71
CO (ppmv) ZPU outlet/ scrubber outlet	660/NA	810/NA	1027/NA	815/NA	640/NA	1765/1670	1055/955
HCl (ppmv) ZPU outlet/ scrubber outlet	NA/NA	NA/NA	NA/NA	NA/NA	NA/NA	1216/1.7	788/2.5
HF (ppmv) ZPU outlet/ scrubber outlet	NA/NA	NA/NA	NA/NA	NA/NA	NA/NA	46/0.24	55/0.86
HNO3 (ppmv) ZPU outlet/ scrubber outlet	NA/NA	NA/NA	NA/NA	NA/NA	NA/NA	56/0.49	127/0.48
NA = Not available

Treatment Effectiveness

The beam dose is the e-beam energy transmitted to the reaction chamber per unit mass of treated gas. The e-beam power was corrected for the 28% window transmission efficiency. The total DRE increases with beam dose, however the NO_x production also increases with beam dose. The electron beam process in this configuration produced 70 to 160 ppmv of NO_x compared with 14 ppmv for other catalytic oxidation systems in operation at McClellan at the time. The maximum total DRE achieved for both soil mixtures was greater than 98%. The data does not satisfactorily conclude whether there is an advantage to H₂O₂ promoter use on DRE and on a reduction in NO_x production.

The effect of moisture on the system is shown by the test runs on 4/6/95 (dry) and 4/7/95 (moisture added), which show that moisture does not have a detrimental effect on system performance. However, when moisture is added there does appear to be a small increase in total DRE and a slight decrease in scrubber outlet NO_x concentration.

System Reliability

Zapit Technology, Inc. reports that the system can be operated reliability, but the lifetime of the reaction chamber window has not been established.

Ease of Operation

It is estimated that an equivalent amount of effort would be required to operate and maintain the e-beam system as a catalytic oxidation unit.

Energy Consumption

Energy consumption would be high for this system.

Space Requirements

This information is unknown since the demonstration was bench scale only.

Worker Health and Safety Issues

A human health risk analysis was performed on the system effluent for gas mixtures 1 and 2, with a 800 cfm flow rate. Table 4 below shows the calculated carcinogenic and noncarcinogenic risks to a resident exposed to the emissions for 350 days per year over a five year period.

Table 4. Carcinogenic and Noncarcinogenic risk to residents from the e-beam technology emissions.
	Carcinogenic Risk	Noncarcinogenic Hazard Index
Mixture 1	8.5 * 10 ^–6	0.14
Mixture 2	4.1 *10 ^–7	0.12

Wastes Produced

The e-beam technology produces NO_x, HCl, HF and HNO₃ as wastes. The scrubber on the demonstration unit was not efficient in reducing NO_x and air pollutant emissions would be a concern for this unit.

Noise/Aesthetics, etc.

Noise levels associated with a full-scale electron beam system could be high due to the presence of various blowers in the system. However, there is not sufficient information available to determine the size, height and noise levels associated with technology since it was only a bench scale study.

Data on Key Parameters

All optimization tests were performed at approximately 3.0 cfm and 175 kV. Applied dose varied from 0 to 20 mA based on changes in beam current.

Capital and Operating Costs

The capital cost and O&M costs were estimated for a single pass e-beam system with a downstream caustic scrubber treating a gas stream of 800 cfm. The cost of the e-beam system is compared to a catalytic oxidation system with a caustic scrubber in table 5 below. The capital and electrical costs are based on a beam dose of 300 J/g and 500 J/g for soil gas mixture 1 and 3 respectively, and a transmission efficiency of 50% for the reactor window.

Table 5. Cost comparison of the e-beam technology and a catalytic oxidation system.
	Mixture 1 ($/day)	Mixture 2 ($/day)
E-beam (single pass)/Caustic Scrubber System Costs
Electricity	616	990
Caustic Solution	175	425
Labor	240	240
Maintenance Materials	44	61
Total O&M	1,075	1,716
Capital	872	1,212
Total	1,947	2,928
Alternative E-Beam/Regenerative Carbon System Costs
Electricity	252	252
Caustic Solution	175	425
Labor	240	240
Fuel	7	7
Maintenance Materials	44	91
Total O&M	718	985
Capital	465	465
Total	1,183	1,450
Cat-Ox/Caustic Scrubber System Costs
Electricity	180	180
Caustic Solution	175	425
Labor	240	240
Fuel	55	55
Catalyst Replacement	9	9
Total O&M	659	909
Capital	228	228
Total	887	1,137

Overall, Zapit Technology, Inc. estimated that the costs for the e-beam system would be 2.2 to 2.6 times higher than for the catalytic oxidation system. The difference in cost is primarily due to greater electrical requirements and greater capital cost for the e-beam system. The vendor suggests that waste streams that do not contain difficult-to-destroy compounds like TCA or freons would require a lower beam dose for treatment and the overall cost for the system would be lower than those see in this study. Further the vendor suggests that when the e-beam system is constructed in combination with a carbon adsorption system, the system could operate at a much lower per-pass DRE and therefore a lower beam does of only 50-125 J/g. A combined e-beam/carbon adsorption system is more cost competitive with the catalytic oxidation system.

Vendor

Zapit Technology, Inc.

3170 De La Cruz Blvd

Santa Clara, CA 95054

408-986-1700

Kevin J. Williams, Ph.D.,

Victor T. Auvinen,

Radian Corporation

10389 Old Placerville Road

Sacramento, California 95827

(916)-362-5332

Radian, 1995, Electron Beam Bench Scale Technical Report, Final, McClellan AR # 2734, August.