Distillation

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Heating System to Prevent Downtime in Distillation Process

Distillation Unit Overview

Limit/Prevent Downtime By Designing Atmospheric/Vacuum Tower Lines for Upset Condition

Continuous Distillation throughput can be limited by operational issues with product solidification (plugging) in interconnecting and downstream piping and equipment. These events, while rare, have historically incurred high cost and lengthy timeframes to rectify – reducing unit profitability.

  1. Distillation units –like most refinery units –maximize profitability through continuous operation. 
  2. As the first step in the refining process, it is a critical gate to overall plant efficiency. 
  3. The general nature of the distillation process is to separate the lighter components of the crude oil supply from the heavier ones –the heaviest of which (bottoms) are drawn off the towers.
  4. FLOWING CONDITION = NO HEAT NEEDED:  Piping and equipment moving bottoms product between towers and downstream processing units typically do not need robust heating systems (in fact, most times no heat input at all) to keep process temperatures within an acceptable range during normal operation.
  5. However, these “heavy” hydrocarbons can present issues when their temperatures are allowed to drop –therefore, ensuring they stay hot is a priority.
  6. With distillation units continuously running ~99% of the time, plugging and other temperature-related process issues are typically seen as anomalies when an upset does occur, and flow stops.  However, these events can have major cost implications to rectify (as the most recent freeze situation in the US Gulf highlighted). 
CSI provides a closer look into these “anomalies” and how heating technology selection, when properly applied, can yield quicker recovery from issues and reduced or eliminated downtime.

Get presentation on Limit/Prevent Downtime By Designing Atmospheric/Vacuum Tower Lines for Upset Condition HERE!

Available Heat Tracing Technology Choices

Tube Tracing           
Traceboost           
ControTrace           

Thermal Objectives for Process Lines and Associated Heating Systems

  • Maintain process temperature above its melt point (flowing condition)

Process movement between as well as downstream of distillation/vacuum columns rarely needs heat during normal operations.  There is inherent heat contained within the processes and the process movement does not require additional heat to ensure flowability.

How far can the process travel without heat?

Bottoms/vacuum residuum flowing through insulated piping without heat

  • Maintain process temperature above its melt point (no-flow condition)

Heating becomes critical when the normal operation is compromised due to an upset and the process stops flowing. Upsets can occur through several causes –including component malfunction such as pumps or other rotating equipment failure as well as loss of utilities. When the upset occurs and process flow stops, BTU delivery is now needed to keep the process liquid and prevent viscosity-related issues from occurring. During these events, the heating system capability is quickly put to the test. 

  1. System must be modelled to add BTUs as needed to keep temperatures above desired minimum
  2. Must consider thermal capability of technology to ensure enough heat input can be achieved to offset losses to ambient and achieve thermal objective.

Heat Loss Chart (stagnant process; no flow)

Design Conditions:

  • 4” NPS pipe
  •  One tracer run of each technology
  • 150 psig steam heating medium
  • 2” thick insulation

Heat Loss Chart in No Flow Condition

  • Melt out process from ambient to normal operating temperature after complete solidification

Requires a robust heating system to accomplish –especially if melt out is desired within a specified timeframe.

Heat Gain Chart (plugged process; melt out)

Design Conditions:

  • 4” NPS pipe
  •  One tracer run of each technology
  • 150 psig steam heating medium
  • 2” thick insulation
Heat Gain Chart