In the energy sector, every moment counts. Ensuring a seamless initiation of plant operations is crucial, and this is closely tied to the procedures followed during plant shutdowns. A deep comprehension of essential shutdown and initiation tactics, combined with an effective anti-corrosion program, is key to avoiding unplanned halts, lowering operational expenses, and enhancing plant dependability. Here’s a comprehensive guide on heating and dehumidification providing a keen insight on saving your power plant from corroding.
A closer look at heating and dehumidification
For plants operating on gas-fired combined cycles, whether they run continuously or cycle frequently, maintaining assets is a primary goal. This is not only vital during active operation but also paramount during standby or shutdown phases. A mere twenty-minute delay can lead to significant financial losses, potentially amounting to tens of thousands of dollars, depending on the scale of your facility and current energy prices. The way you safeguard your equipment during dormant periods significantly influences the time it takes to restart, overall plant efficiency, and the likelihood of unexpected operational interruptions.
Poor lay-up processes
These failures include condenser leaks, turbine deposits, boiler tube damage due to corrosion fatigue or hydrogen transport, and corrosion product transport in feed water heaters. Implementing a well-planned strategy ensures smoother operations.
This strategy should consider the plant’s downtime duration, the available time for shutdown, the urgency of resuming operations, and the desired speed of startup. Lay-up approaches vary based on different shutdown and start-up conditions at each plant, but protecting against corrosion is crucial, regardless of whether the plant is idle for a few hours or several months. Safeguarding the water treatment systems is essential, including zero liquid discharge systems, open and closed loop cooling systems, and evaporative air coolers, to reduce start-up time.
How to prepare a plant for inactivity?
The approach to preparing a plant for periods of inactivity varies based on the duration of the shutdown. These periods are generally categorized as follows: in accordance with the Power Purchasing Agreement (PPA), or spanning hourly, daily, weekly, or more than a week. For short-term shutdowns, often ranging from an hour to a day, as seen in hot lay-ups, it is important to keep a minimal pressure and ensure the right cycle chemistry. Additionally, maintaining a vacuum in the condenser is crucial to preserve the correct steam seal. In scenarios of wet lay-up, typically needed from a day to a week, it is essential to keep drum levels and turbine vacuum, while also maintaining a nitrogen or steam blanket.
Regular testing is a must for all wet chemistry methods. For extended shutdowns, it is advisable to drain the Heat Recovery Steam Generators (HRSGs) while they are still hot, which involves completely emptying the hot well. The turbine should also be kept at a certain relative humidity level to avoid common issues arising from improper lay-up. Measures should be taken to safeguard sample panels and analyzers as well.
Water Treatment Machinery
To safeguard water treatment machinery against deterioration, cycle water from the output of filter to the input of clarifier. This keeps the machinery operational, and the pumps engaged. The recirculation rate, typically between 20-50% of the volume, should be adjusted accordingly.
Day tanks need to be turned off, cleaned, and the appropriate blowdown level for the clarifier should be established. Filters should be backwashed and stored full of water and bleach solution for extended shutdowns. Cartridge filters must be removed, and their housing cleaned. It is essential to operate Reverse Osmosis (RO) systems daily with a biocide to prevent biofouling. During seasonal breaks, membranes should be detached, stored in a 1% bisulfite solution, and bagged.
Chemical tanks and pumps require cleaning. Mixed bed systems can remain unused for a few days, but it is best to run them alongside the RO unit for maintaining water quality over short periods. For long-term or seasonal shutdowns, regenerate these systems at the end of the season, ensuring separation of cation and anion beads in mixed beds. Before restarting, air out the mixed beds.
Cooling Towers
In maintaining cooling towers, it is crucial to consistently apply biocide each day and keep track of the outcomes in the open loop system. Although it is possible to lessen the use of scale and corrosion inhibitors, ongoing corrosion checks are essential during periods of inactivity. For extended shutdowns, empty and cleanse the basin of the cooling tower, along with examining and, if required, fixing or substituting spray nozzles. Also give importance to inspect and cleanse open water boxes. The condenser tubes should be cleaned, and sacrificial anodes examined, replacing them when needed. Regarding evaporative air-coolers, draining and cleaning the drain sump is necessary, as well as inspecting the media for any signs of fouling, slump, shifting, or damage. Should the damage be considerable, replacing the media is recommended.
Extended Storage
When preparing for extended storage, manage chemical storage carefully. Typically, bleach is still added to systems, but tanks used for other purposes need to be emptied and cleaned. Buy bleach in smaller amounts and store it away from sunlight, as its effectiveness can diminish due to exposure to heat, light, and UV radiation.
For acid tanks, it’s crucial to ensure that the vents and vent dryers are functioning to prevent moisture ingress. Regular checks of the caustic tank heaters are recommended, and using nitrogen blankets might be beneficial to exclude CO2, which can lower the caustic’s effectiveness due to moisture. Additionally, chemical pumps used for non-essential products should be detached, cleaned, or overhauled as needed.
Active and Inactive Protection Methods
Products that form films (PFF) and amines that create films (AFF) serve as substitutes for both active and inactive protection methods. PFFs and AFFs create a thin, water-repellent layer that separates the metal surface from liquid or steam conditions. This protective coating allows protection from corrosion caused due to exposure to oxygen, carbon dioxide, and moisture.
It can enhance traditional lay-up methods and offer additional protection in challenging environments in certain operational units like Air-Cooled Condensers (ACC). These products have demonstrated their effectiveness in adapting to the evolving operational patterns of units, such as unpredictable shutdown durations, fluctuating loads, and quicker start-up times.
In the power sector, each second counts, especially during plant start-up, which is crucial for efficient operations. The success of starting up and the overall functioning of the plant are closely tied to the procedures used during lay-up. Implementing well-documented procedures and making the required equipment adjustments are key to a seamless start-up and lay-up process.
Looking for an Expert?
Worry not! TDS Asia is here to guide you through each step of prevention from corrosion in your power plant. We are an experienced dehumidification rental service which has highly trained experts on board. Devoting adequate time to these processes is essential. Hence, plan your next prevention drive with us. Remember! Even a short delay of about 20 minutes could lead to significant financial losses, potentially amounting to tens of thousands of dollars, depending on the scale of your operations and current power market rates. Save your valuable time and money by relying on TDS.
