New Alternatives to Online DPD Instruments for TRO Measurement in BWMS

1. 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 from 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.

2. Executive Summary

The DPI Amperometric sensor is a new alternative to online DPD instruments. When used in Ballast Water Management Systems (BWMS), this alternative eliminates potential compliance issues with unique features:

3. Third-Party Evaluation (ACT)

The Alliance for Coastal Technologies (ACT) conducted an evaluation of Ballast Water TRO instruments with currently available technology[ACT HF, 2020][ACT HSI, 2020][ACT Xylem, 2020]. While ACT did not directly compare sensors, several key points are evident from these reports:

4. Fast Response from Direct Pipe Installation

This sensor is installed directly in the ballast pipe for rapid TRO readings (under 1 minute). 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.

5. 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.” To demonstrate the robustness of this sensor, it was evaluated using 40 times the required TSS level (2,000 ppm)[HSI ISO15839, 2020].

6. 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 to 1.93 m/s to 3.73 m/s. Sensor accuracy was checked using a laboratory spectrophotometer (Hach DPD) for total chlorine measurement[HSI 06, 2020].

Table 3: Flow Test — Hach DPD vs. Halogen Sensor

From these data, it is clear that flow conditions have a negligible effect on sensor accuracy between 0 and 3.73 m/s flow velocity.

7. Low Operational Cost

No chemical reagents or membranes are needed, resulting in lower-cost operation and maintenance labor by the ship’s crew. There is only a bi-annual wear kit replacement. According to KRS, DPD instruments also require additional maintenance operations[KRS].

Table 4: Cost Comparison — DPI Amperometric vs. DPD

8. 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[HSI 04, 2020].

Table 5: Field Test Assumptions — Typical BWMS Maintenance Period

During a typical two-week voyage, a ballast/deballast cycle occurs in which the sensors run for approximately 8 hours and remain off for the rest of the voyage. The sensor would have been recalibrated if at any time it deviated from the DPD reading by 15% or more. No recalibration was needed throughout the entire test period.

9. 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. Estimated savings are over $2,200 per instrument.

Table 6: Comparison of Installation Costs

* Data from customers

10. 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. The four-step process includes: (1) close the valve, (2) retract the sensor via the removal point, (3) slide the sensor out of the remover plate, and (4) disconnect the saddle clamps from the junction box for quick replacement.

11. Hazardous and Non-Hazardous Models

There are four sensor models available. Both Hazardous (Zone 1, Group IIC) and non-hazardous model types are available with three mounting options: in-pipe (hot tap), side stream, and open deck.

The sensor’s smaller size and rapid removal make it suitable to carry as a spare on board, reducing potential downtime. The sensor is easily separated from the junction box for quick replacement or service.

12. Self-Cleaning

The sensor is covered by seven US patents and five foreign patents. The integrated pump 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 moves them 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.

13. Integrated Salinity Sensor

All sensors come with an integrated salinity sensor. This may reduce the need for another instrument (savings of over $3,000). This function enables sensor compensation in freshwater ports.

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