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TP1208EN.docx Jun-15

SUEZ helps refineries to save time, reduce energy consumption, emissions and waste by efficient decontamination Authors:

Donato G. Vinciguerra

André Vanhove

Marc Verschoren

abstract

Energy savings, environmental compliance, and health and safety precautions, whilst maintaining or improving the refinery profitability, are key factors for refineries; especially in the current difficult economic environment.

Efficient chemical cleaning/decontamination can be integral to this by providing the following benefits:

• Reduced total shut down time

• Reduced steam consumption

• Obtain “Gas Free” equipment much quicker

• Reduced time for mechanical cleaning

• Reduced waste generation

• Environmentally friendly products

The type of cleaning to provide optimum results depends on the unit configuration, fouling mechanism investigation and deposit analyses.

SUEZ has developed a program to obtain efficient decontamination and to reach the targets for H2S, aromatics and LEL in the various refinery process units in preparation for the unit shutdown.

The procedure includes a complete chemical cleaning and monitoring program for degreasing, degassing

and the removal of pyrophoric products; with the objective to avoid or minimize mechanical cleaning requirements of refinery equipment.

introduction

To perform maintenance on refinery equipment, prior conditioning work is required to allow safe working in an adequate health protected environment. Very often refineries invest a significant amount of time and energy to obtain the "gas free" unit required to enter the equipment for inspection and maintenance work. Despite the invested time, the equipment pre-conditioning is not always successful and additional time is required before the equipment is ready.

SUEZ has developed and introduced chemicals and procedures to the refining industry in order to reduce the time required to prepare the equipment, by enhanced pyrophoric material removal and ensuring "gas free" conditions are obtained when opening the equipment.

Through the knowledge gained from decades of monitoring and chemical treatment on hundreds of refineries around the world, SUEZ is fully aware of the mechanisms and types of contamination present in each refinery unit. Based on this SUEZ has also developed various types of customized chemical products (brand name: Custom Clean) and chemical cleaning procedures, allowing in many cases, to minimize or dispense the mechanical cleaning.

This paper will explain in depth the SUEZ technology applied during chemical cleaning and decontamination in refinery equipment, including: type of fouling, type of chemical cleaning, physical

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and chemical mechanisms of the chemical cleaning and results/benefits obtained.

types of contamination

The type and amount of contamination present in the refinery equipment can be very different, depending on the process section, quality of the feedstock, time and severity [1] of the operation etc. For this reason, each cleaning needs to be individually designed, based on the expected contamination present in each of the equipment sections.

Some examples of the different types of contamination that can be found in refinery units are shown below:

Crude Unit

• Exchangers upstream of the desalter (cold preheat train): fouling is mostly the result of salts and particulate precipitation with potentially some corrosion products.

• Desalter: fouling is typically is composed of corrosion products and particulate organic material from upstream, with additional precipitation of organic material caused by crude incompatibility. Depending on the wash water quality used, carbonate scaling and precipitation can also be encountered.

• Exchangers downstream of the desalter (hot preheat train): many different fouling mechanisms can be encountered depending on the temperature level. Polymerization reactions result in organic deposition, often enhanced by heat. Other organic and inorganic contaminants can lose their solubility as the temperatures increase and precipitate in the equipment.

• Crude Tower Preheat Furnace: furnace fouling or coking is common when significant preheat exchanger fouling is encountered.

• Atmospheric column has typically no significant fouling issues above the flash zone. It is common to find fouling due to iron sulfide and corrosion products.

• Overhead Condensers: ammonium and/ or amine salt deposition with corrosion products like iron sulfide and iron chloride are typically encountered

Hydrodesulfuration Unit

• Preheat train fouling: is typically caused by polymerization reactions together with corrosion products (i.e. iron sulfide) and other solids present

in the feedstock.

• Effluent Fouling consists normally of ammonium chloride and ammonium sulfide salts; eventually with corrosion product formed by under deposit corrosion.

• Hydrogen Recycle Compressor may be due to ammonium chloride, ammonium sulfide, or iron sulfide deposition.

Sour water stripper

• Feed HX: solids and corrosion products from upstream equipment entrained with the feed.

• Tower (internal and bottom): caused by carbonates precipitation and corrosion products from upstream equipment.

• Tower Overhead: ammonium bisulfide, polysulfide, elemental sulfur (if air is present) and deposition of corrosion products.

• Reboiler end effluent HX: is typically the result of polymerized hydrocarbons of phenols present in the feed and the deposition of corrosion products from upstream equipment.

In the same way that the units described above, each of the refinery units such as FCCU, VB, DCU, Alkylation, Merox Unit, Amine Unit, etc., have, different types of contamination in each of the unit sections, which requires a customized evaluation to define the appropriate chemicals and cleaning procedures to obtain the best results.

types of chemical cleaning

The chemical cleaning procedures during a major shut down consist typically of two types of cleanings: the liquid phase and vapor phase chemical cleaning (decontamination) [2].

Steam Chemical Cleaning (SCC) or Decontami-nation is performed to remove the volatile organic components and inorganic solids such as iron sulfide producing volatile toxic gasses. The objective is to reduce the required steam-out time before entering the equipment

The SCC or decontamination phase in intended to prepare the equipment to a “gas free” state, which is minimum required for safe entry into the equipment for inspection and/or other activities. The gas free condition is obtained when reaching the following concentrations:

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H2S < 1.0 ppm Aromatic ~ 0 LEL ~ 0

Successful SCC have been performed in different equipment such as fractionation columns in Crude units, vacuum units, FCCU, visbreakers, HDS, LC finer, lube units, amine units, selexol units, heat exchangers, separators drums etc. In general, in all equipment where typically a standard steam-out procedure is applied during the shutdown, the steam chemical cleaning provides a significant benefit in reducing the required time to obtain “gas free” equipment, a lower quantity of steam is required for the cleaning and better overall results are obtained.

Chemical Cleaning in liquid phase is performed when SCC alone is not sufficient to remove the fouling or deposits. Depending on the type of contamination and the objective of the cleaning, the liquid phase chemical cleaning could contain one or more of the following steps:

Degreasing: is performed for the removal of organic substances with medium and high molecular weight and mud and is applied as the first step in the chemical cleaning process. The degreasing step is commonly used in CDU, vacuum units, visbreakers, FCC Slurry, storage tanks. In general degreasing is applied in hydrocarbon processing units where the precipitation of asphalthenes, waxes and coke particles is suspected to have caused fouling during the operation.

Degassing: is performed to remove light hydrocarbons such as benzene, toluene, xylene, light gasoline, etc., from the equipment. The degassing step is also used for the removal of hydrogen sulfide and inorganic volatile salts (i.e. ammonium salts). The objective of this phase is to obtain the equipment “gas free” to allow entering the equipment.

Acid Cleaning (pH controlled): The acid cleaning step is used to remove strong inorganic deposits such as carbonates and sulfates of calcium and magnesium, as well as for the total removal of iron sulfide deposits. This cleaning step should be applied in units or equipment where maintenance activities will be conducted requiring flame cutting, welding, etc.

chemical cleaning procedure

Based on the information provided by the refinery, the chemical cleaning specialized engineer needs to determine which of the different cleaning steps are required to ensure the expected results are obtained.

The recommended cleaning procedure for each specific application includes the following activities:

• Define the steam injection points • Select the chemical and dosage. • Define type and frequency of analysis • Define loop for cleaning. • Evaluate the availability of utilities. • Define disposal strategies. • Estimate the time required to perform the

cleaning. • Support the field structure to develop all the

chemical cleaning process as appropriate.

In the case where the application of one or more steps of chemical cleaning in the liquid phase is required, the specialized engineer will also evaluate how the effluent could be managed to minimize the impact on refinery operations. In co-operation, with the refinery, the chemical cleaning steps are optimized to maximize the reuse or reprocessing in the refinery processes and minimize potential waste generation.

The final procedure for each cleaning step needs to be agreed and approved by the refinery maintenance personnel, operations, process engineering, and health and safety responsible before being implemented.

chemical cleaning mechanism

The removal of fouling from substrate (Equipment’s wall) involves several mechanisms acting individually or in synergy [2,3,4].

The chemical cleaning of a fractionation column, contaminated with high levels of hydrocarbons, iron sulfide and hydrogen sulfide, would require the chemical capability to modify equipment walls by wetting metal surface to remove the liquid hydrocarbon adsorbed at the equipment metal surfaces. Once removed from the surface, it is necessary to keep the hydrocarbons solubilized or emulsified to be removed from the system with the aqueous phase.

For iron sulfide, the cleaning process begins with desorption of the solid material from the substrate

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(equipment wall). Simultaneously, the deposit needs to be kept in suspension by surfactant or chelating agents. The released hydrogen sulfide need to be trapped in water solution by a solubilizing and scavenging mechanism.

Depending on the type of deposit and the substrate the required cleaning mechanisms include:

Surface Wetting: mechanism for removing liquid hydrocarbons from the equipment walls.

In a typical case, as shown in Figure 1, the substrate (S) is covered with a liquid organic fouling layer (O), and both are in an aqueous environment (W). The angle θ corresponds to the contact angle between the hydrocarbon (O) and the metal surface (S) and is in general called θOS. Likewise, the contact angle between the water (W) and S is θWS (= 180 ° - θOS).

If θOS << 90 °; the metal surface remain covered with the organic liquid.

Figure 1.

The chemical (Custom Clean* product), induces the effect of droplet contraction, called "rolling-up" (see Figures 2 and 3). This will significantly reduce the contact area between the liquid hydrocarbon and the substrate and enhance the removal of the HC droplet from the equipment wall. The chemical has a significantly higher affinity for the metal surface than the hydrocarbon.

Figure 2.

Figure 3.

When the wetting of the metal surface is completed θWS is close to 0°, and the hydrocarbon drop can easily detach from the metal surface either by gravity or by turbulence in the aqueous phase.

Solid Desorption

The mechanism of removal of solid fouling particles from a substrate is completely different compared to liquid contamination. Adhesion of the chemical on the metal surface and solid particles is based on the combination of Van der Waals attractive forces and electrical repulsive forces between the treated metal surface and the solids deposited on the metal surface. Custom Clean products penetrate between the deposit and the metal surface, reducing the attractive forces and enhancing the removal of the solid particles; thus reducing the energy requirement and using the turbulent conditions in the system.

In Figure 4 are the different steps to remove solid contamination from a metal surface are shown.

Figure 4.

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Solubilization: In aqueous solutions, Custom Clean products are designed to form micellar solutions that significantly increase the solubility of hydrocarbons in aqueous phase, (figure 5). Hydrocarbons type components are typically non-polar substances and are captured in the core of the micelles, which consists of the lipophilic portions of the surfactant molecules.

Figure 5.

results obtained – case studies

In the last few years SUEZ has performed chemical cleaning and decontamination applications in many refinery equipment and units. These procedures have been very successfully applied in equipment such as: CDU fractionation columns, vacuum units, FCC, visbreaker, HDS, LC Finer, lube, absorption and desorption columns in gas sweetening units (amine and selexol units), heat exchangers and many separators drums. In general, the chemical cleaning and decontamination has offered a significant benefit in terms of reducing the steam-out time, savings in steam requirements, mechanical cleaning time and finally reducing the total shut down time.

Crude Unit Atmospheric Tower decontamination

A Southern refinery needed to reduce the time needed to obtain the “gas free” conditions in the crude unit atmospheric tower. During the last 3 planned shutdowns more than 96 hours were required to reach the conditions to be able to enter the column. Due to the type of crude oil processed and the typical operating conditions a preliminary washing followed by steam cleaning was required. Additionally, pyrophoric residual products were still observed on the column internals and to prevent ignition risks, a

continuous water injection was maintained to keep the deposits wet until the total removal was obtained with the mechanical cleaning.

A decontamination procedure was proposed, using only the steam out phase and a Custom Clean product was injected with the steam. The operator observed the steam condense drained from the system was becoming very black when the Custom Clean product injection to the steam was started; indicating that a lot of deposit material had been removed.

Analysis of sulfide, total suspended solid, ammonia and hydrocarbons were performed on the steam condensates at different critical locations. After 24 hours the condensed water became bright and clear and the analysis indicated that most of the pyrophoric compounds, ammonia and hydrocarbons were removed in all areas of the column which were identified as being critical for the cleaning performance.

The total time of the steam out procedure was reduced from over 96 hours to less than 36 hours. After the required safety controls the tower was ready for inspection. Refinery engineers found the tower very clean and no additional mechanical cleaning activities were necessary.

CDU: Atmospheric Tower Cleaning

A Central European refinery expected a lot of fouling in the crude unit atmospheric tower bottom section for the next turnaround. Deposits from the atmospheric residue transfer pump were analyzed and results indicated 40% ash (mainly FeS & FeSO4) and 60% carbon black type compounds.

At another refinery in the same group experienced a fire during the shutdown due to FeS, requiring special attention for the cleaning application. The refinery requested SUEZ to design a chemical cleaning procedure with specific focus on FeS removal.

A 3-step cleaning procedure was proposed, based on a degreasing, degassing and an acid cleaning procedure. The refinery decided to only apply steps 2 & 3, because in the period before the shutdown only light crudes will be processed and the unit condition is expected not to require the degreasing step. In addition, before the chemical cleaning started, the unit was rinsed with naphtha.

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The Custom Clean degassing product was added to the water and applied during the once through water-rinsing and steam-out phase to remove the light hydrocarbons. The rinse water and steam flow were adjusted to obtain a continuous controlled water flow out of the bottom drain, and a steam plume through the top vent. It was observed that the water drain became very black once the Custom Clean degassing product was injected into the rinse-water, confirming the removal of a lot of deposit material from the system. After 3 hours the water rinse became bright and clear, indicating that most of the hydrocarbons were removed.

Subsequently an acid cleaning with a Custom Clean product was applied during a 4-hour in a closed water circulation loop at ambient temperature, and all solid Fe-salts became water-soluble. The rinse water again became very dark during the draining, indicating that carbon black type compounds were removed as a result of breaking the bond between the by Fe-salts and the organic deposits. An additional water rinse was applied to remove the acidic solution.

After the required safety controls the tower was ready for inspection. Refinery engineers found the tower very clean and no additional mechanical cleaning was required.

Figure 6 and 7 are pictures from the tower internals showing the clean condition of the tower internals after the SUEZ chemical cleaning was completed.

Figure 6.

Figure 7.

Amine Unit Chemical Cleaning

At a Southern European refinery the amine absorber tower was fouled, such that during the next refinery shut down a mechanical cleaning of the tower was scheduled.

The absorber fouling was mainly caused by the presence of “Black shoe polish” type deposits. A high DP of the column and poor performance in terms of H2S removal were encountered. “Black shoe polish”, is a common fouling material encountered in amine systems and is essentially gelled or pasty slurry of iron sulfide which adheres to all surfaces. This material can be removed by a properly designed surface wash with a water based Custom Clean solution.

For this cleaning, the “Off-line Cleaning” procedure for Amine Gas Removal Systems was applied. Several options for cleaning the absorber were considered, including water washing, chemical cleaning and mechanical cleaning. The SUEZ program was decided based on total cost, required manpower and cleaning time, including safety and environmental considerations.

The results of the cleaning was evaluated based on the amount of material that could be removed from the tower from a series of washes and then finally

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by a visual inspection during the equipment opening.

In accordance with the procedure, a Custom Clean aqueous solution was circulated. The circulation was applied at 60 °C for 4 hours. This step was repeated 5 times. Samples were taken for analysis during each step.

Based on sample results, the amount of removed solids was more than 1 ton. The effluent water from the unit was sent to the wastewater treatment system of the refinery without problems.

When the absorber was opened (see figure 8); no fouling was present. Similarly, no fouling material was found in the flash drum of the system (see figure 9) or in the regenerator.

The customer confirmed the cleaning to be very successful and was adopted as best practice to be used for future requirements.

Figure 8.

Figure 9.

summary

Reduction of the required cleaning time during scheduled maintenance shutdowns, reducing energy consumption, ensuring the safe operation and minimizing the environmental impact is experienced to be an important objective of refineries in the current economic environment. SUEZ, having extensive experience of chemical treatments and monitoring of fouling phenomena in all the refinery units, has developed chemicals and specific procedures to perform effective cleaning and unit decontamination, which have exceeded the expectations of major refining groups in Europe.

references

[1]. Betz Process Chemical, Inc., “Refinery Technical Reference Manual”, Chapter 4, August 1988.

[2]. Vinciguerra Donato G.; Vanhove André.; “Equipment Chemical Cleaning Manual”, SUEZ W&PT Library, June 2014

[3]. Salager Jean-Louis “Detergencia Fenomenos y Mecanismos” Cuaderno Firp-ULA S331-A (1988)

[4]. Salager Jean-Louis “SURFACTANTS Types and Uses” FIRP-ULA BOOKLET # E300-A (2002)