Oct-2006

Vacuum heater installation

One refinery has proved it is possible to revamp any process unit by modification and/or replacement of key process equipment in situ

Giampiero Caronno
Foster Wheeler Italiana SpA

Article Summary

The JSC Mozyr oil refinery in the Republic of Belarus recently completed the installation of a new vacuum distillation heater, which had been assembled directly within the 
1 800 000 tpy vacuum distillation (UVDM) unit.

With a challenging schedule of 12 months from contact signature to start-up, the 350-ton fired heater fabricated module was moved onto existing foundations. Careful project planning meant it was possible to achieve the installation in less than 30 days, well within the scheduled vacuum unit turnaround. The newly installed fired heaters dramatically improved the process unit performance.

On 3 November 2005, the UVDM unit was started up after a scheduled unit turnaround lasting less than 30 days. During this turnaround, the existing fired heater was replaced with the custom-designed Foster Wheeler furnace in order to optimise process operations and ensure that all process requirements, and environmental and refinery demands were met. A detailed analysis was carried out with refinery management, process unit operators and mechanical specialists.

Foster Wheeler had previously supplied the refinery with a new visbreaker heater. The JSC Mozyr oil refinery took this into account during the evaluations and analysis for a new heater supplier, together with the fact that Foster Wheeler had the capability to carry out this type of refurbishment. Detailed knowledge of all aspects of heater design was an extremely important issue. Factors to be taken into consideration included:
•    Plot space for lifting
•    Logistics for modules access and egress for plant and heavy equipment
•    Lay-down and working areas.
These factors had to be considered during the initial planning and evaluation phase of the project due to their potential impact on cost and schedule. Prime challenges for the project team were:
•    Project timing This was critical, as the turnaround had already been defined as October/ November 2005, less than two years after the commencement of feasibility studies
•    Feasibility of the project Since the vacuum unit shutdown period was short, the construction work had to be completed in the shortest possible time, thereby minimising production losses.
In the preliminary analysis, cost-effective and innovative solutions were identified to safely undertake the replacement of the fired heater in the shortest time. These solutions ranged from in situ modifications to full unit replacement. The ideal solution was to effect a full fired heater unit replacement, but with the following restrictions:
•    Modifications of process and utilities piping had to be reduced to a minimum, with no changes to existing foundation piers
•    A new vacuum heater needed to be designed to maintain the new foundation loads within the allowable values
•    The existing steam recovery system through which the flue gases left the convection section had to be modified, and the new heater convection section had to take this factor into account.
A proper tie-in on flue ducts was required, since the flue gases were to be sent to the existing concrete stack through the flue gas ducting system already in place.

After careful analysis of the various options, JSC Mozyr oil refinery personnel were confident that the proposed total revamp was possible and work commenced (Table 1). The new furnace was to be erected in the area next to the existing fired heater, which needed to be kept in production and operation until the last day before turnaround.
 
Main process parameters
Among the various factors driving the revamp and replacement of the vacuum heater, there were several process considerations and problems relating to the operation and efficiency of the existing furnace. The radiant surface of the original heater was insufficient. Therefore, the heat flux was too high when compared with the heat flux value of 25 500 W/m2, which is generally utilised for current vacuum heater installations.

The vertical disposition of the radiant tubes of the original heater was a critical configuration for the flow pattern inside the process coil, with local overheating and high coke build-up in the zone where vapourisation occurred. The tube size and the process fluid velocity were inadequate and the heat-transfer co-efficiency was very low, with a high fluid film temperature and coke build-up as a consequence.

The new design was developed on the basis of the available existing plot area, and took into consideration the installation of a mixed configuration of vertically and horizontally disposed coils. The new heater was designed to present standard and codes, and offered the following advantages:
•    Longer operating periods without decoking
•    Tube size properly selected, taking into account the process fluid velocity
•    Radiant surface designed according to 25 500 W/m2 heat flux max
•    Reduction of maintenance activities for long periods
•    High efficiency. Table 2 highlights the estimated fuel saving based on 8000 hours/year
•    Very short payout period due to both the fuel saving and refurbishment costs of the existing heater
•    Reduction of NOx emission into the atmosphere.
Table 2 highlights the following process factors and parameters pertaining to the vacuum heater:
•    Same absorbed process duty
•    Lower heat fired and consequently lower fuel consumption
•    Lower radiant heat flux and consequent milder furnace operation
•    Lower excess air
•    Lower flue gas emissions.

Project initiation
The JSC Mozyr oil refinery awarded Foster Wheeler Italiana SpA a fixed-price lump sum contract for engineering services and the supply of critical equipment for the refinery on 14 October 2004, following a bid declared in compliance with Belarussian law. There were two immediate major challenges, which related to project timing and project feasibility: