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Solvent blend to unplug the bottoms of a quench water tower in an ethylene plant

IP.com Disclosure Number: IPCOM000249697D
Publication Date: 2017-Mar-21
Document File: 3 page(s) / 120K

Publishing Venue

The IP.com Prior Art Database

Related People

Jorge H. Pazmino: INVENTOR [+6]

Abstract

This work highlights the advantages of using blends of an aromatic solvent with a dimethyl phthalate (DMP) bases commercial solvent to detach and displace heavy tars from the bottom of a quench water tower. The tars accumulated in a cone-shaped separator and are normally in contact with process water at 80-90 °C. The use of aromatic solvents alone proved not to be effective due to the short contact time with the tars. This is caused by the displacement of the (lighter) organic solvent by the (heavier) aqueous phase. Laboratory experiments demonstrated that blends of a commercial aromatic solvent with a tar breaker that is denser than water were effective in removing tars. Temperature, contact time and blend composition were varied to understand the range of applicability of this concept to the tower in the Dow ethylene plant.

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Solvent blend to unplug the bottoms of a quench water tower in an ethylene plant

J.H. Pazmino, M. Brayden*, S. J. Korf**, D. Flick, E. Frank, J. Hamilton

(Dow Chemical, Freeport) (*Dow Chemical, Plaquemine) (**Dow Benelux B.V.)

Abstract

This work highlights the advantages of using blends of an aromatic solvent with a dimethyl phthalate (DMP) bases commercial solvent to detach and displace heavy tars from the bottom of a quench water tower. The tars accumulated in a cone-shaped separator and are normally in contact with process water at 80-90 °C. The use of aromatic solvents alone proved not to be effective due to the short contact time with the tars. This is caused by the displacement of the (lighter) organic solvent by the (heavier) aqueous phase. Laboratory experiments demonstrated that blends of a commercial aromatic solvent with a tar breaker that is denser than water were effective in removing tars. Temperature, contact time and blend composition were varied to understand the range of applicability of this concept to the tower in the Dow ethylene plant.

Introduction

A quench water tower is a unit operation in an Ethylene plant that serves the purpose of cooling the cracked gas coming from the furnaces by direct contact. In this particular tower, the water and heavy hydrocarbons flow to the bottom of the tower to a cone-shaped section that helps separate the organic and aqueous phases from the heavier solids. In normal operation, the flow of process water leaving the bottom of the funnel carries the heavies to a hydrocyclone to remove the solids from the water that is recycled back to the tower. Over time tars accumulated at the bottom of the cone and caused several plugging events in the water circulation loop. Injections with ExxonMobil solvent Aromatic 150 were ineffective in unplugging the cone. Hydroblasting was effective for the outside piping but was not able to remove the tars inside the tower cone, which caused plugging to recur soon after. Alternatives to mechanical cleaning required injection of a solvent that would detach or dissolve the tars without the need of vigorous mixing or flow conditions.

Typical approach to solve the problem.

US patent 7,282,136 B2 and application EP 1,751,258 A2 filed by Nalco claimed the use of halogen-free, water-immiscible, heavier than water organic solvents for cleaning processes. Mixtures of dimethyl phthalate (“DMP”) with phenols, maleic acids, and anisoles were included. The invention describes the injection of solvent at the top of the tower or into the reflux to dissolve the heavier components. The patent claimed dosage ranges from 10 ppm to ~ 5 wt.% of the solvent diluted with unsaturated aromatic hydrocarbons co-injected to the tower with the returning quench water. The treatment can be used in a batch or continuous mode.

Alternative approaches to solve the problem.

Laboratory tests with tar samples from the QWT bottoms of a Dow ethylene plant and the DMP-based solvent from Nalco were co...