Steam Tracing Rationalisation

Steam tracing is heat tracing that uses steam as the heating media. This can be saturated low pressure (LP), medium pressure (MP), or high pressure (HP) steam. The condensing temperature can be about 150-180 degC (for LP steam), 200-215 degC (for MP steam) & 250-270 degC (for HP steam). Pressure levels vary from refinery to refinery.

Steam for tracing is supplied to the individual steam tracing circuits with the help of steam supply manifolds . Condensate is evacuated through properly designed pipeline connectors. and tracer line traps, collected at condensate collection manifolds and finally transferred to condensate headers through steam operated pump traps..

Critical tracing

Critical tracing or steam jacketing is a unique concept wherein the core pipe is surrounded by another pipe. Steam enters and travels through the annular space between the two pipes, transferring heat across the whole cylinder surface to maintain a closed temperature profile. The heating medium comes directly in contact with the entire surface of the process pipe, providing the maximum surface area for even heating.

In the steam jacketing process, heat is transferred through convection coefficient enabling maximum thermal capability for high ΔT difference.

Rationalisation

Rationalisation is the concept of identifying the right steam pressure to make product tracing cost-effective and productive. It provides suitable steam pressure to maintain closed temperature profiles and maximises the usage of latent heat as per the characteristics of the product which is being traced.

The table below gives an idea of products requiring steam tracing to maintain product temperature at >90 degC. Considering all factors of safety and design, it is advisable to use low-pressure steam (3.5 to 4 barG) for tracing these products.

Product Name	Required Temperature
HVGO	> 90 ° C
HFLO	> 90 ° C
LVGO	> 90 ° C
PFL	> 90 ° C
RCO	> 90 ° C
Slops	> 90 ° C
VGO	> 90 ° C
VR	> 90 ° C
VS (Vac Slops)	> 90 ° C

Objectives of steam rationalisation

To identify existing and possible scenarios of steam connections for the tracing network
To check the feasibility of providing low-pressure steam connections for existing steam tracing network
To analyse existing steam tracing network for correct pressure and temperature
To provide suitable economical alternate options in existing steam tracing network
To optimise the steam consumption for the steam tracing network
To suggest corrections in existing steam tracing network for efficient performance.

Case Study

The crude oil distillation unit of a petroleum refinery was using medium pressure (18 barG) steam as a tracing medium. Most times, medium pressure steam is superheated and has a low heat transfer co-efficient, hence not recommended for tracing applications. Saturated steam is ideal for tracing and heating purposes.

After a detailed study of the system it was established that the heat requirement for these products can be satisfied by providing low pressure steam at 5 barG while maintaining the same number of steam tracers. These stations were therefore provided with LP tracing steam to rationalise and optimise steam consumption.

The low pressure steam contains higher latent heat and has optimum heat usage, which helped to reduced the net steam consumption.