Chemical Cleaning Service
Sheppard T. Powell Associates, LLC (STPA) has provided independent consulting services since 1921 and laboratory services since 1970 to power plants, pulp and paper mills and other plants with boilers or HRSG units. At some point, STPA has been involved in virtually every aspect of chemical cleaning related to the following.
- Preoperational Flushes and Chemical Cleaning
- Chemical Cleaning Assessment
- Solvent Selection
- Site Assessment
- Chemical Cleaning Hydraulic Evaluation
- Chemical Cleaning Procedure
- Technical Specifications/Request for Bid Documents
- Bid Evaluation/Procedure Finalization
- Execution of Chemical Cleaning Process
- Documentation Critique
STPA has considerable experience in the planning and execution of chemical cleaning activities for power boilers, recovery boilers, once-through steam generators, Benson boilers, and Heat Recovery Steam Generators (HRSGs). STPA also has assisted in chemically cleaning a generator stator cooling water system. STPA authored for EPRI three versions of the Guidelines for Chemical Cleaning Conventional Fossil Plant Equipment (CS-3289, 1984; TR-102401, 1993 and TR-1003994, 2001), the Evaluation of Solvent Processes for Chemical Cleaning of Supercritical Waterwalls and Removal of Duplex Oxides Formed by High-Temperature In Situ Oxidation of Ferritic Steels (TR-1020882, 2010), and the Chemical Cleaning Guidelines for Fossil-Fuel-Fired Power Plants (TR-3002000996, 2015) for EPRI. Additionally, STPA co-authored the Heat Recovery Steam Generator (HRSG) Chemical Cleaning Guidelines (TR-1004499, 2003) and the Heat Recovery Steam Generator (HRSG) Chemical Cleaning Case Studies, Final Report (TR-1012756, 2006) documents for EPRI. STPA has presented seminars and training programs on various chemical cleaning topics.
Preoperational Flushes and Chemical Cleaning
STPA visits the site to review HRSG or boiler drawings, available flush and chemical cleaning connections, existing piping, flush and solvent circulating path(s), water supply options, steam supplies, space limitations, and site conditions for the preoperational flushes and chemical cleaning activities. Procedures, temporary piping systems and other required preparations for the preoperational flushing and cleaning are developed by STPA. The STPA technical team is present during the preoperational flushing and cleaning processess to monitor the flushing and cleaning activities, respond to questions, and advise on the means of addressing unforeseen situations.
Chemical Cleaning Assessment
STPA will advise where to collect a tube sample for evaluation. The STPA laboratory can analyze the tube sample conditions, waterside deposit weights and deposit compositions. From the HRSG or boiler design, maintenance and operating history, and laboratory data, STPA can establish the desirability or necessity to chemically clean the unit.
Based on chemical cleaning assessment, STPA can develop a solvent formulation(s) and determine whether a single stage or multistage solvent exposure is required for removal of the waterside deposits. In the laboratory, a section of the tube sample is exposed to the selected solvent formulation(s) until the tube waterside surface is clean. From the laboratory test, the final solvent formulation(s) and exposure period are confirmed. The potential composition of the spent solvent(s) also can be determined.
STPA visits the site to review HRSG or boiler drawings, available chemical cleaning connections, existing piping, solvent circulating path(s), water supply options, steam supplies, space limitations, and site conditions. If requested, STPA also can discuss and assist in the evaluation of waste handling and disposal options.
Chemical Cleaning Hydraulic Evaluation
STPA can develop circulation flow paths and flow rates through the various HRSG or boiler sections based on the recommended fluid velocity in the evaporator or boiler and economizer tubes. STPA can recommend suitable capacity and other criteria for the circulation pump(s), heat exchanger(s) temporary piping, chemical feed equipment, etc. The calculations will determine the quantity of chemicals and temporary storage tanks required for the chemical cleaning.
Chemical Cleaning Procedure
Before preparation of a Request for Proposal (RFP) document, the chemical cleaning method, details of the chemical cleaning process, temporary piping system and other required preparations are developed by STPA. Additionally, water supply and waste solvent storage requirements are formalized. Sometimes, STPA will provide projections of the range of spent solvent compositions. The results of these activities aid in both the design and preparation of schematics for the temporary piping system along with a detailed chemical cleaning procedure and timeline. The chemical cleaning procedure helps to ensure that the solvent is properly applied and introduced to the appropriate sections of the component being cleaned.
Technical Specification/Request for Bid Documents
An RFP provided by power plants to the prospective chemical cleaning contractors must include a technical specification. STPA has developed technical specification documents to be used as an enclosure for RFP packages for our clients. Information in the technical specification includes background on the facility, the required solvent formulation(s), chemical cleaning timeline, contractor-supplied equipment and services, qualifications of contractor personnel, contractor responsibilities, and planned manner of spent solvent disposal. The specification often defines the requirements for PPE and other safety measures, preparations to enable effective response to solvent spills, waste handling/treatment plan(s), and analytical protocols.
Bid Evaluation/Procedure Finalization
STPA evaluates the technical content of the chemical cleaning contractor bids and provides an assessment of the degree to which each bid conforms to the bid specification. Once a chemical cleaning contractor is selected, a meeting with all concerned parties is convened to review the chemical cleaning procedure, tour the site, and select locations for the chemical cleaning equipment and portable storage (Frac) tanks.
Execution of Chemical Cleaning Process
The STPA technical team is present during the cleaning process to monitor the cleaning activities, respond to questions, and advise on the means of addressing unforeseen situations. STPA personnel maintain a detailed event Log of Operations throughout the chemical cleaning process. The STPA level of involvement depends on the wishes of the client. STPA has been requested by clients to manage the entire onsite chemical cleaning process. Alternatively, some clients prefer to utilize STPA in a more advisory capacity to supplement and assist plant personnel through the process.
Once the chemical cleaning is complete, STPA’s Log of Operations is formalized. Some clients elect to ship a sample of the spent solvent(s) to the STPA laboratory for analysis and comparison with results obtained during contractor field analyses. As part of the STPA report, any necessary equipment or procedure changes either incorporated during the cleaning process or deemed desirable for future cleaning operations will be highlighted. A general critique of station and contractor preparations and performance for the cleaning process also will be provided.