Solving the flow control challenges in ethylene: Part 1

Increasing supply of plastics to meet demand while reducing emissions to hit net zero targets requires the industry to review their processes and operations.

Lindsay Coutinho
Director Refining and Chemicals, Valmet

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Article Summary

As the world population surges toward the 10 billion mark, the demand for plastics is due to increase exponentially. In this first blog, we explore the requirements of this rapidly evolving industry and application, and the flow control solutions available to facilitate future developments.

Meeting growing demand responsibly
This suggests that petrochemical production will also have to ramp up to meet this demand while aligning itself with the net zero targets set by the industry. Licensors, engineering consultants and end users are constantly reviewing their operations and processes toward achieving this objective, the majority by 2050, the rest by 2060 or 2070 at the latest.

Ethylene is the largest and most versatile building block in the petrochemical industry. Ethylene production alone is expected to reach a market size of $287 billion by 2030, as reported by Statista.

Changing with the times
As demand for refining transportation fuels goes down under the net zero regime, many refineries are reconfiguring themselves into integrated refining and petrochemical complexes, with chemical conversion rates ramping up from 10 to 25%. Technologies from crude oil to chemicals are targeting even higher conversion rates, ranging from 70 to 80%.

In the past, many petrochemical companies, particularly in the Middle East and North America, have been working with low-cost natural gas feedstock. However, looking ahead, the industry will be looking more toward liquid feedstocks, such as naphtha.

Expense of meeting flow control requirements
Ethylene is produced by cracking, i.e., the hydrocarbon feedstock is heated at temperatures in the region of 800 degrees Celsius, either with steam or more recently electrification heating, the result being separated into valuable products like ethylene: propylene, acetylene, butadiene, pyrolysis gasoline and BTX.

In a typical petrochemical complex, housing most of the units mentioned above, flow control solutions – valves and pumps – constitute a reasonable share of the total CAPEX of USD ~1 to 3 billion. In addition, process performance, safety, reliability and product quality are heavily influenced by the valves, particularly automated on/off, emergency shutdown (ESD) and modulating control valves.

The purpose of this article is to provide the reader with a perspective on the automated valve selection approach that will enable the fulfillment of the abovementioned objectives while providing cost-effective CAPEX and OPEX.

Understanding the process and requirements
An ethylene cracker can be broadly divided into three sections, viz. Hot Zone – where the actual cracking and subsequent cooling occurs; Compression Zone – where the effluent is compressed, scrubbed and dried; and the Cold Zone – where the different components are separated from the medium.

An ethylene steam cracker can accept a variety of feedstocks, including naphtha, ethane, propane and gas oil. The choice of feedstock depends on the cracker furnace construction, the availability of the feed, its current market price, and the desired end products.

In a traditional steam cracker, the feed is diverted to multiple furnaces via multiple passes before entering each furnace. In the subsequent convection section, dilution steam is injected into the furnace tubes to protect the pipes from fouling or forming coke. The hydrocarbon-to-steam ratio should therefore be optimised to achieve optimal flow conditions. The flowrate of the steam depends on the severity of the feed. Steam can also be used for decoking the furnace.

The process system in an ethylene cracker must supply the correct amount of raw material to produce the desired end products.

The right valves for the job
The steam control valve must therefore have high rangeability, while the feedstock supply valve must have accurate controllability, taking into consideration that in some cases, the feedstock can be a liquid, and a gas in others. As the flowrate difference between low flow and full capacity can be significant, some ethylene producers use separate valves for each case.
Globe control valves have a strong position when it comes to controlling the dilution steam in cracker furnaces.

Adding rotary valves to the offering, such as a V-ported segment or eccentric plug, gives more opportunities for reliability and cost optimization. They are effective choices especially for sizes of 3 in. and larger, and for applications with sticky flow media and particles present, such as coke and heavier hydrocarbon feedstock.

Rotary valves also enable a reduced cost for piping, cabling and other connections, especially where wide rangeability means they offer the possibility of eliminating the use of split range control and a secondary valve in the piping.

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