SigmaClean Prepares the Watersides of the Heat Recovery Steam Generator (HRSG) for Operation
Systems to be prepared for the operation will be:
Boiler Feedwater Pumps
HP/LP Evaporators and Drums
Boiler Feedwater System
BEST's proven method of washing and passivating the internal surfaces of Heat Recovery Steam Generators (HRSG), uses operational chemistry with no hazardous waste while simultaneously testing Boiler Feed Pumps to baseload.
The concept behind SigmaClean is to convert reactive iron surfaces to a passive state, similar to what would be present on the surfaces after extended running in normal operation. To do this, BEST circulates a solution of demineralized water with all volatile chemistry at elevated temperatures to condition the watersides of the HRSG for operation.
The all volatile chemistry creates an elevated pH and oxygen-depleted environment that promotes the formation of the passive form of iron oxide - Magnetite. Magnetite, an inorganic polymer, has extremely low solubility in demineralized water. High pH is also effective in removing any light oils present from the manufacturing and assembly process. The all volatile chemistry is compatible with all components in the components being cleaned, including the Boiler Feed Water (BFW) pump.
Figure 4 - Fully Passive Drum Internals
The elevation of temperature is created by operating the BFW pump at full operating flow and pressure. The mechanical energy transferred to the fluid by the pumps will raise the temperature of the circulating solution to above 212°F (100°C). Operating the BFW pumps at these conditions enables the commissioning of these pumps concurrently with the SigmaClean process, significantly earlier than normal, off the critical path and before steam operation of the HRSG.
A temporary filtration system is also provided to remove contaminants present in the waterside components of the HRSG. Combined with the high rate of circulation and elevated temperatures, it is particularity effective in cleaning the tubes and lower headers .
Once elevated temperatures are achieved in the HRSG by circulation, it is maintained along with chemistry for a minimum of 24 hours and is not stopped until the following is achieved:
• Full conversion of the internal surfaces to magnetite is verified by analytical methods
• BFW pump suction strainers return no particulate
SigmaClean has been proven effective in eliminating the requirement for aggressive chemical cleaning where acids or chelants are applied, generating waste streams that require offsite disposal.
SigmaClean Eliminates the Need for:
• Large staging areas – no elaborate pumping equipment, heat exchangers, steam generators, piping, or hoses are necessary
• Extensive flushing – only two boiler volumes of demineralized water are required for SigmaClean.
• Chemical disposal – SigmaClean uses that same all volatile chemistry as used during normal operation of the HRSG and produces waste similar to concentrated blowdown. No chemical disposal and the associated extensive batteries of frac tanks to stage and rig.
The Result: an HRSG with clean and passivated watersides that produces no BFW strainer trips during the steam blow.
Chemistry is easily achieved and maintained during operation due to the superior passivation provided by SigmaClean.
Quotes from the VGB 513e Guidelines on Chemical Cleaning
“Treated surfaces shall be free from deposits and other contaminants. Residual layers shall be guaranteed to be less than 20 g/cm .”
“Pre-operational cleaning is the chemical cleaning of a new plant prior to initial start-up. Depending on the surface condition and start-up specifications the selection of the appropriate pre-operational cleaning procedure depends on various individual factors. Taking environmental loads, required surface cleanliness, steam purity to be obtained within a certain time, and last, but not least the economic efficiency into account, the choice may be made between various pre-operational cleaning methods. It is advised to perform pre-operational cleaning whenever the number of deposits exceeds 100 g/m .”
“Operational cleaning is the removal of deposits accumulated during operation. Depending on the extent and composition of deposits, material condition, and operational requirements of the plant user, in each specific case, shall make a choice between chemical cleaning and re-tuning. It is recommended to perform chemical cleaning if the number of deposits in the evaporator exceeds 500 g/m on the heated internal tube surface of the pressure loss has clearly increased.”
So Let's Ask These Questions
What is the amount of mill scale or deposits on a new HRSG?
What is the specification set forth on your project for acceptable deposits on the boiler when purchased?
Is it possible your new HRSG, just received at the project came with < 20 g/m ?