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Innovative Approach to the Control of Vacuum Collection, Holding and Transfer (VCHT) Foaming


OBJECTIVE: To develop an innovative approach to detect and control or eliminate foaming in sewage VCHT tanks and systems onboard naval ships without the use of biological or hazardous materials. DESCRIPTION: Currently used DDG 52 AF Class sewage VCHT systems are highly susceptible to foaming. Foam can be generated in the VCHT tank due to the combination of liquid and solid human waste, freshwater flushing and detergents being re-circulated through the ejector pump and ejectors at high velocities. VCHT tank vents, which are under atmospheric pressure (14.7 pounds per square inch gauge (psig)), are vented to the weather decks onboard ship. Once foam enters the tank vent and tank overflow piping in sufficient quantity to prevent the venting of pressure and hazardous fumes from the tank, pressure builds up inside the tank as a result of frequent in-rush of sewage and air from the ejector pumps. The tanks become pressurized (approximately 15 20 psig and at some point force the foam from the tank out through the tank vent onto the weather deck (Ref 1). In addition, the foam clogs sensors, and causes premature pump failure due to the easily cavitating foam in the ejector pump. Traditionally, foam generation inside VCHT tanks has required Ship"s Force to: a) deactivate the sewage collection system; b) flush and clean the VCHT tanks, which is time consuming and often ineffective; c) increase ejector pump corrective maintenance (repair) as a result of the damage from foam, which is costly, dangerous and impacts system availability. Previous attempts at resolving this issue have resulted in numerous engineering modifications to reduce the occurrence of foam generation in VCHT tanks and subsequent spills through the tank vents. While changes to date have effectively segregated plumbing waste from the VCHT tanks, foam reduction due to these actions has not been adequate and continues to be an un-resolved issue of concern. In the commercial maritime industry, some Marine Sanitation Device (MSD) manufacturers recommend pouring diesel fuel in to the VCHT tanks to mitigate foaming, but this method is neither recommended nor approved since it introduces oily waste into a sewage system, which is regulated by different discharge standards. This topic seeks to explore the development of innovative approaches to detect and mitigate the effects of foam generation in sewage VCHT tanks (Ref 2 and 3). Proposed concepts must be non-biological and non-hazardous, should provide an indication of when foam is detected inside VCHT tanks and should mitigate, by control and/or elimination, the effects of foam on sewage collection system operations. While foam detection is not the sole focus of this topic, it is important for several reasons. In practice, a foam mitigation system may not be required to function at all times during VCHT tank operation, but only during times when foam generation has been detected. Additionally, the ability to detect the presence of foam is important in order to be able to determine the effectiveness of the foam countermeasures proposed. Proposers should address proposed candidate processes, materials, equipment(s), and manufacturing processes, as applicable, as well as methods of installation anticipated to enable the development and integration of a detection and mitigation solution(s). Specifically, concepts proposed should contribute to a reduction in corrective maintenance and total ownership costs as well as improving system availability and may be considered for application on LPD 17 Class, LCS-1 and LCS-3 VCHT systems as well. PHASE I: Demonstrate the feasibility of the development of an innovative approach(es) to detect and counter-act VCHT foam generation or otherwise mitigate its effects in VCHT tanks and systems based on the requirements above. With an emphasis on counter-acting foam generation, the company will demonstrate the feasibility of the concepts in meeting the Navy needs and will establish that the concepts can be feasibly developed into a useful product for the Navy. The feasibility demonstration will include Rough Order of Magnitude (ROM) cost estimates for system acquisition, daily operation and maintenance requirements, system size and how it would be integrated on a VCHT Tank as well as a notional commercialization plan and will identify any potential safety hazards associated with the proposed concepts. The company will provide a Phase II development plan and schedule with performance goals that contains discrete milestones for product development and will be utilized to verify candidate concept(s) performance and suitability. PHASE II: Based on the results of Phase I and the Phase II development plan, the company will develop a scaled prototype for evaluation. In a laboratory environment, demonstrate that the prototype system meets the performance goals established in Phase I. Perform a safety analysis of the modified system and any consumable materials and identify any potential safety hazards associated with the proposed concepts. Provide a detailed Phase III development plan for certification, validation, and method of implementation into a future ship test and/or design environment. Prepare refined cost estimates for system acquisition, daily operation and maintenance requirements as well as logistics data packages, and interface documents for use in both forward fit and retrofit ship programs. Refine the commercialization plan. PHASE III: Upon successful completion of Phase II, the company will work with government and industry, as applicable, to construct a prototype based on the Phase II results for testing in a shipboard environment. The full-scale prototype will then be installed onboard a selected DDG 52 AF class hull and extended shipboard testing will be conducted. Upon successful completion of the testing, validation, certification and qualification requirements, the technology will be incorporated for use onboard naval ships as practicable. The company will support the Navy for test and validation to certify and qualify the system for Navy use. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: These systems are installed in most modern warships, cruise ships and other commercial cargo or personnel carriers. Any vacuum collected non-oily wastewater (including sewage) system will also have foam-generation issues and should benefit from the developed product.
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