By: PI-Energi Technology Manager / Process and Corrosion Engineer, Manik Priandani
Pupuk Indonesia Energi (PI-Energi) is a subsidiary of PT Pupuk Indonesia (Persero). Engaged as a utility producer in the form of electricity and steam (steam). PI-Energi's plant is the Gresik Gas Cogeneration Plant (GGCP) which is located in the Gresik Petrochemical Industrial Estate, East Java. In addition, PI-Energi also has a majority stake in Kaltim Daya Mandiri (KDM) which is located in the East Kalimantan Fertilizer Industrial Zone in Bontang.
Currently, Electricity and Steam PI-Energy products are used as energy, lighting, as well as raw materials for the production process for fertilizer factories in Pupuk Indonesia (Persero). One of the most important equipment in the process unit at the PI-Energi plant is a Boiler.
Boilers are used to heat water and prepare and produce steam. There are various variations of boiler types depending on their use. Boilers are also classified according to their structure, water circulation method, type of fuel, and the type of material used.
The boiler system can be divided into three parts according to its location, namely Preboiler, Boiler and Post Boiler. The preboiler includes a feedwater pump, pipes, and auxiliary equipment through which the feedwater passes. Since being pumped until it reaches the Boiler (the make up water system as a stabilizer system is not included, the Stage Heater and Economizer are part of the Preboiler). The Boiler System is the Boiler itself, while the Post Boiler includes the Superheater, Condenser and return system.
The problem often experienced by boilers is corrosion. With regard to boiler material, boiler treated media, water-containing environments as well as high boiler operating temperature and pressure conditions. Until now, boiler material still uses a metal base material, namely iron. In aqueous environment, conditions of high temperature and pressure and humid conditions, metals tend to experience corrosion. Corrosion can cause thinning to the point of holes in the metal surface. Can be fatal if not addressed.
The analogy that can be presented is as follows, when we boil water in a kettle or pot, over time crusts will appear. Either on the surface of the lid or in the pot or kettle. Likewise with boilers operating in steam plants. The sticking scale will accelerate the corrosion rate of the boiler. Leakage due to corrosion, especially under the invisible crust is very risky because the boiler is under pressure.
In general, boilers are available in several operating pressures. First is a low pressure boiler (less than 20 kilograms / cm2). Second, medium pressure (20-75 kg / cm2. Third, high pressure (above 75 kilograms / cm2). This short article will explain three problems that can potentially occur in boilers that have different pressures in relation to scale, corrosion and carry problems. over.
The first problem is sediment. Often also called deposits or crust. In general, it is closely related to the byproducts contained in the metal when the sludge is dispersed in the boiler water. It can easily spread evenly over the metal surface because it is easy to move or may be a binding agent for scale. The effect caused by the accumulation of sludge from various alloy tubes resulted in corrosion attack on carbon steel (conventional boilers such as in GGCP) and Monel (Boiler nuclear powerplants).
Prevention is to remove the scale by pretreatment. Among other things, using an ion-exchanger (Mixed Bed Resin) to eliminate dissolved solid ions. Ion exchange materials (resins) currently used generally use synthetic organic material exchangers.
Various corrosion attacks can occur in the boiler. These include pitting corrosion, cavitation and erosion. Pitting corrosion is caused by conventional causes, namely dissolved oxygen, low pH, presence of sediment, stagnant areas, stress on metals and defects in metal composition or surface.
Dissolved oxygen often causes pitting attacks when paired with certain conditions such as deposits on metal surfaces or metal defects. Oxygen will oxidize the ferric hydroxide film to magnetite (Fe3O4) or to become ferric oxide hydrate. Oxidation occurs at a certain distance from the metal, which causes more iron to dissolve on the surface beneath the porous corrosion product. The pH value is the main cause of corrosion in general.
The composition of the water passing through the feed pipe may be distilled water or demineralized water converted to soft water or tap water, either in acidic or alkaline conditions. The temperature varies from ambient (room) temperature to temperatures close to the boiler temperature. K