New Alternatives to Online TRO Measurement
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New Alternatives to Online DPD Instruments for TRO Measurement_in_RIA/MS
2020
Background
Halogen Systems, Inc. started in 2012 to commercialize its multiparameter sensor technology. From the outset, it sought to eliminate the problems with existing amperometric sensors and develop a robust, alternative
sensor platform with applications across many industries. Its sensor is radically different other sensors, hence its name, DPI (Direct Pipe Insertion) Amperometric. This new amperometric sensor was funded, in part, by
Small Business Investment Research (SBIR) contracts from the US Office of Naval Research (ONR) (DoD, 2020). Since 2014, this sensor saw constant improvement and enhancement. Performance and relative
advantages are described in the sections below:
Executive Summary
The DPI Amperometric is a new alternative to Online DPD Instruments. When used in Ballast Water Management Systems (BWMS), this alternative eliminates some potential compliance issues. Unique features include:
- Direct measurement of TRO in ballast pipe for faster response (<45 seconds).
- Robust and accurate operation in muddy ports.
- Accurate operation at 6 times the DOC (Dissolved Organic Carbon) challenge levels that BWMS are tested to.
- Flow Independent- Accurate operation while experiencing ballast flow changes.
- Models available for Hazardous and Non-Hazardous, Open Deck, Side Stream, and Ballast Pipe installation.
- The sensor works reliably at 20 times the TSS (Total Suspended Solids) levels, or greater, required by ETV (1000 ppm) without any filters.
- Integrated salinity measurement eliminates the cost of a discrete salinity sensor.
- Integrated pH sensor can withstand 10 bar and -0.7 bar and is stored dry.
There are also installation and service cost advantages:
- Requires no skid mounting, sampling lines, filters, pumps, waste line, or remote valves for lower installation costs and simpler operation.
- Uses no Reagents, membranes, or electrolyte.
- In a Field Test the sensor operated for the equivalent of 15 months without maintenance or calibration.
- Uses both mechanical self-cleaning and electrochemical cleaning for low maintenance.
- Wear parts are replaced every two years for low maintenance costs.
- A new Hot Tap Valve Removal Tool makes this sensor easier to install, remove, and replace.
Extensive Validation in BWMS application:
- In a recent ACT TRO Sensor evaluation, this amperometric sensor proved comparable in performance to Online DPD units.
- There are over 2,000 of these sensors installed in BWMS on vessels since 2014.
- DNV Type Approvals are in issued.
Third-party evaluation
The Alliance for Coastal Technologies (ACT) conducted an evaluation of Ballast Water TRO Instruments with currently available technology. While ACT did not directly compare sensors, several points are evident from these reports.
- In the precision test, (comparative results are listed in Table 1 below), brand-new DPD instruments, installed by factory personnel, were both out of their respective specifications of 5% (below 6ppm). The DPD1 accuracy during the precision test was ±15%, while DPD2 was ±32%. Halogen was well within its specification at ±4%. Its Standard Deviation was better (2.5% vs. 2.6%) than the DPD Reference Method.
- One DPD Instrument did not operate properly during two of the Accuracy Tests in Table 2, hence no data could be collected. Note: numbers closer to 1.00 are better.
- In the Accuracy Tests, DPD and HSI sensors performed similarly or better than DPD instruments (for the tests for which there were data).
PSU Salinity
HSI
DPD1
DPD2
0.2
0,809
0,809
1.072
0.2
0.962
0,809
0.728
0.2
0.814
0,924
0.777
15
0.779
--
0,762
15
0.825
0.783
0.458
15
0.793
0.859
0.635
30
0.756
--
0.746
30
0.818
0.747
0.456
30
0.717
0.787
0.603
15
Not Tested
0.814
0.585
16
0.778
0.794
0.665
Sample Reading
Reference Method
DPD2
DPD1
HSI
1
3.55
2.3
3.02
3.45
2
3.56
2.41
3.1
3.45
3
3.48
2.39
3.01
3.4
4
3.53
2.39
3.01
3.34
5
3.49
2.29
3.05
3.34
6
3.5
2.3
2.93
3.35
7
3.47
2.31
2.92
3.33
8
3.41
2.33
2.91
3.28
9
3.38
2.32
2.85
3.27
10
3.45
2.3
2.83
3.24
11
3.33
2.32
2.79
3.22
12
3.27
2.27
2.68
3.2
Average STDEV CV (%)
3.45
0.09
2.60%
2.33
0.04
1.90%
2.93
0.12
4.20%
3.32
0.08
2.50%
Relative % Accuracy
-32%
15%
15%
Fast Response from direct pipe installation
This sensor is installed directly in the ballast pipe for rapid TRO readings (<1 min). Online DPD instruments fed by long water sampling lines introduce potential sample contamination as well as a delay (often 3 to 8 minutes on some vessels) before the BWMS receives an updated reading. A delayed process loop often causes problems with accurate control, resulting in oscillation between over chlorination and under chlorination. Long sampling lines are also often responsible for sample contamination.
Robust Operation in muddy ports
BWMS systems are evaluated using a challenge level of 50 ppm Total Suspended Solids (TSS) (EPA, 2010). However, some ports have much higher suspended solids and the water can even appear “muddy.” As ballast tanks are emptied, silt remaining in the bottom of the tank has a similar effect. To demonstrate the robustness of this sensor, it was evaluated using 40 times the required TSS level (2,000 ppm) (HSI ISO15839, 2020). These high TSS levels adversely impacted the DPD method (Spectrophotometer) resulting in lower measurements. This is apparent from Figure 2and Figure 3. To obtain accurate DPD readings the sample required: 1) reaction with the reagent, 2) filtration (5 micron) of the sample to remove the TSS, then 3) measurement. (Hach, 10014). This resulted in both filtered and unfiltered DPD measurements for each TRO level. These should align since the TRO concentration is the same for both samples, however, they start diverging at 200 ppm of TSS, indicating the dirty water is interfering with the spectra in the measurement method.
An online DPD instrument suffers from the same limitation. As seen in Figure 3, lower TRO discharge levels (like the critical Maximum Allowable Discharge Concentration (MADC) of 0.1ppm) result in an even more significant reduction in accuracy.
Ballast water Flow rate changes have no impact on measurement accuracy
Other amperometric sensors are extremely sensitive to flow changes. Halogen’s sensor has proven flow independence. During this test, flow varied from 0, 1.93 meters per second velocity (m/s) to 3.73 m/s. Sensor accuracy was checked using a laboratory spectrophotometer (Hach DPD) for total chlorine measurement. The sensor measured chlorine accurately at all three flow rates (See Table 3). Figure 4 shows these results (HSI 06, 2020).
Hach DPD values with corresponding Halogen sensor measurements from the time the water sample was taken. The accuracy of the Halogen sensor as compared to the Hach DPD value is given in the last column.
low Operational cost
No chemical reagents or membranes are needed, resulting in lower-cost operation and maintenance labor by the ship’s crew (Table 4). There is only a bi-annual wear kit replacement. According to KRS, DPD instruments also require additional maintenance operations (Korean Register of Shipping (KRS)):
Flow Test
Flowrate (GPM)
Chlorine Concentration (ppm)
Hach DPD
Halogen Sensor
Accuracy of Halogen Sensor
0
8.98
8.96
0%
8.83
9.05
2%
120 (3.73 m/s)
9.49
9.06
-4%
9.48
9.04
-5%
9.02
8.94
-1%
62 (1.93 m/s)
8.64
8.99
-4%
9.06
8.89
-2%
8.87
8.92
1%
0
9.26
8.92
-4%
9.23
8.82
-4%
120 (3.73 m/s)
8.09
8.77
-1%
9.29
8.91
-4%
9.04
8.77
-3%
Flow Test (continued)
Flowrate (GPM)
Chlorine Concentration (ppm)
Hach DPD
Halogen Sensor
Accuracy of Halogen Sensor
62 (1.93 m/s)
8.9
8.8
-1%
9.02
8.91
-1%
8.78
8.84
-1%
0
8.61
8.78
2%
9.05
8.78
-3%
120 (3.73 m/s)
8.77
8.7
-1%
8.82
8.63
-2%
9.14
8.61
-6%
62 (1.93 m/s)
8.96
8.67
-3%
8.71
8.71
-0%
9.07
8.55
6%
0
808
8.63
-2%
8.77
8.48
-3%
From these data, it is clear the flow conditions have a negligible effect on sensor accuracy between 0 and 3.73 m/Sec flow velocity.
Long interval between Maintenance cycles
Following the ISO 15839 methodology for a “Field Test” Halogen Sensors operated 24 hours a day, for a total of 33 cycles over 80 days, yet required no maintenance or calibration. This corresponds to 66 weeks or 1.2 years of shipboard operation and over 792 hours of actual sensor operation. This accelerated test was based on assumptions shown in Table 5. During a typical two-week voyage, a ballast/deballast cycle occurs in which the sensors run for ~8 hours and remain off for the rest of the voyage. During the deballast cycle sodium sulfite was used as a chlorine neutralizer to lower the TRO level ~0.1 ppm. Chlorine levels were measured at several points during the deballast cycle, including at 0.1 ppm. The sensor would have been recalibrated if at any time it deviated from the DPD reading by 15% or more. An example of a cycle is shown in Figure 5 (HSI 04, 2020).
Service
DPI,Amperometric
DPD
Reagents
None
Reagents every 30 to 60 days of operation
Replace Wear parts
24 months
NA
Annual Costs USD
$120
~$600
Annually
NA
Pump requires overhaul every year due to corrosion by chemicals and seawater
Monthly
NA
Checking and Cleaning T-strainer
Quarterly
NA
Checking and Cleaning check valve and pump tubing
Semi- annually
NA
Two-way solenoid valve cleaning
Installation cost
Installation costs for the Halogen Sensor are much lower than DPD instruments since there are no sampling lines, waste lines, remote valves, sample conditioning, or pumps (See Table 6). Estimated savings are over $2,200 per instrument.
Tyoical BWMS Maintence period
Typical Voyage (days)
14
Ballasting Time per Voyage (hours)
10
Ballasting Time per month (hours)
21.4
Calibration Check (days)
60
Typical Sensor Operation (hours) in 60 days
42.9
Ease of Service
The Halogen Hot Tap Valve allows for easy sensor mounting in a ballast pipe and can be equipped with a removal tool for either permanent attachment or intermittent service.
Figure 6 Sensor installed without optional Remover
Figure 7: Remover installed to retract sensor to:
1. Valve close point
2. Then removal point
Figure 8: Slide sensor out of the Remover plate
Figure 9: Remove saddle clamps to separate sensor from junction box
Item
DPT Instrument
Amperometric Sensor
Cost Comparison
Pump
909
0
Valves
Waterlines Run shipboard
Skid mounting
Sample conditioning and filtration
1,763
0
0
0
0
Hot Tap Valve & Remover
NA
0
Total Added Installation Cost
$2672 Estimated
0
Hazardous and Non-Hazardous Models
There are four sensor models available. Both Hazardous (Zone1 Group IIC) and non-hazardous model types are available with three mounting options. The sensor’s smaller size and rapid removal make it suitable to carry as a spare on board, reducing potential downtime (See Figure 10). The sensor is easily separated from the junction box for quick replacement or service Figure 9. A side stream version is also available that does not require pressure or flow regulation (See Table 8). Customers have installed this version without a sampling pump by using a pressure differential in the ballast pipe to circulate water through the chamber. The models can also be installed on Open Deck.
Item
In Pipe (Hot Tap)
Side Stream
Non-Hazar
Self-cleaning
The sensor is covered by seven US Patents and five foreign patents. The integrated pump Figure 11 increases velocity across the sensor electrode surfaces and increases the signal, thereby increasing the signal to noise (S:N) ratio. This feature also makes constant cleaning of the electrodes possible. Cleaning beads are captured in a cavity within the sensor the flow and moves them about to abrade the electrodes. This pump is driven by a motor with a 20,000-hour life. In addition to TRO, the sensor measures salinity, temperature, ORP, and pH. Three of these parameters are used to compensate for signal changes in fresh and brackish water.
Item
IECEX Sensor
Side stream chamber with IECEx sensor with sampling port
Hazardous-Zone1 Group IIC
Integrated salinity sensor
All sensors come with an integrated salinity sensor. This may reduce the need for another instrument (savings of >$3,000). This function enables sensor compensation in freshwater ports.
Conclusion
As stated in the 2014 report (Tamburri, 2014): “Amperometric sensors are not commonly used in BWMS but offer some potential advantages over other instruments. Amperometric sensors are reagentless and if applied to BWMS would allow for the direct immersion of the sensor in a sampling inlet, ending the need for sampling pumps and reagents associated with DPD online analyzers.”
Designed specifically for BWMS type applications, Halogen’s amperometric sensor is a unique combination of technologies that serve the Ballast Water applications in a cost-efficient manner eliminating some potential compliance issues.
References
Alliance for Coastal Technologies HF. (2020). PERFORMANCE VERIFICATION STATEMENT For the SSR-Ex Total Residual Oxidant (TRO) and Chlorine Monitor. Baltimore, MD: Alliance for Coastal Technologies. Retrieved from (http://www.act-us.info/evaluations.php
- Alliance for Coastal Technologies HSI. (2020). PERFORMANCE VERIFICATION STATEMENT For the SWN-P Total Residual Oxidant (TRO) Sensor: Halogen Systems. Baltimore, MD: Alliance for Coastal Technologies. Retrieved from (http://www.act-us.info/evaluations.php
- Alliance for Coastal Technologies Xylem. (2020). PERFORMANCE VERIFICATION STATEMENT For the Model 9017 Total Residual Oxidant (TRO) Analyzer: OI Analytical/Xylem. Baltimore, MD: Alliance for Coastal Technologies3. Retrieved from http://www.act-us.info/evaluations.php
- DoD. (2020, July 07). SBIR-STTR-Sucess: Halogen Systems, Inc. Retrieved from sbir.gov: https://www.sbir.gov/node/1704083
-
EPA. (2010, September). GENERIC PROTOCOL FOR THE VERIFICATION OF BALLAST WATER TECHNOLOGY. Retrieved from United States Coast Guard
: https://www.dco.uscg.mil/
Portals/9/ETV%20EPA%20Report.pdf?ver=2018-05-22-081043-607 - Hach. (10014). Method 10014. Chlorine Total USEPA 2 to 500µg/L Cl2.
- HSI 03. (2020). Amperometric Sensor Turbidity Performance. White Paper 03.
- HSI 04. (2020). Halogen ISO 15839 Field Test. White Paper 04.
- HSI 06. (2020). Amperometric Flow Sensor Test Report. White Paper 06.
- HSI ISO15839. (2020). ISO 15839 Final Report- Halogen Sensor. Incline Village.
- ISO, 2. 1. (2003). Water Quality - Online Sensors/Analysing Equipment for Water - Specifications and. Geneva, Switzerland: International Organization for Standardization.
- Korean Register of Shipping (KRS). (n.d.). BWMS Technical Information for Shipowners and Inspectors (translated). Busan, Republic of Korea.
- Tamburri, Z.-F. A. (2014). Evaluation of approaches to quantify total residual oxidants in ballastwater management systems employing oxidants in ballastwater management systems employing. Water Science and Technology, 1585-1593.
- WP111 Halogen Systems, Inc. (2020). New Alternatives to Online DPD Instruments for TRO Measurement in BWMS. Incline Village, NV: Halogen Systems, Inc.
