Project ZAK – Grupa Azoty

Project Overview

Terephthalic acid (PTA) is a fundamental raw material used widely in the industry, including the production of PET and advanced plasticizers. When Grupa Azoty ZAK S.A. launched a new non-phthalate plasticizer, they built a production plant with a capacity of 50,000 tons/year.

For this major investment, Wakro Sp. z o.o. was entrusted with designing and constructing a comprehensive system for the unloading, storage, pneumatic transport, and dosing of terephthalic acid.

 

The Industrial Challenge

Handling PTA involves overcoming significant physicochemical and environmental hurdles:

• Explosion Risks: PTA is a white powder with explosive properties, characterized by high maximum pressure and explosion dynamics.

• Harsh Reactor Conditions: The continuous dosing system had to feed the PTA directly into an esterification reactor operating under extreme conditions: high temperatures, organic chemical vapors, and negative pressure.

• Material Buildup: PTA is soluble in organic compounds. Feeding loose material under these hot, vapor-rich conditions causes it to accumulate on the inner walls of the feed pipes, which narrows the cross-section and can lead to severe blockages.

• Pressure Fluctuations: Reduced pressure inside the reactor could cause the uncontrolled suction of material, disrupting the continuous, uniform feed rate required for high-quality production.

Wakro’s Solution: Safety and Innovation

To ensure a highly efficient and safe process, our engineers divided the technological line into tightly controlled unit processes:

1. Safe Unloading and Storage

The raw material is delivered in specialized Beut 82 Uacns rail tankers. Unloading into the storage silos is performed via a flexible pneumatic transport hose and a compressed nitrogen hose. To guarantee absolute safety, a dedicated control and measurement system continuously monitors the pressure in the silos and immediately interrupts loading if safe values are exceeded.

 

2. High-Pressure Pneumatic Transport

For moving the material from the outdoor silos to a buffer tank inside the production hall, Wakro utilized an overpressure pneumatic transport pipeline.

• The bulk material is fed through a rotary feeder and a screw conveyor into a chamber feeder.

• The high-pressure transport is executed using a specialized chamber feeder protected by patent PL219232.

• The entirely airtight installation prevents any material dusting into the environment, which eliminates the creation of secondary explosion hazard zones in the hall.

3. Innovative Continuous Dosing Module

To overcome the reactor’s harsh conditions, Wakro designed and manufactured a brand new dosing module.

• The module integrates a weighing tank, a mechanical screw feeder, and advanced control and measurement electronics.

• It features a specific set of devices designed to continuously clear the feed line and compensate for the negative pressure inside the reactor.

• As a result, the system achieves the ultimate goal: continuous, uniform dosing of terephthalic acid at a constant rate, adjusting dynamically to uneven process conditions.

ATEX Compliance and Inerting Systems

Because PTA dust and liquid organic compound vapors can form a highly dangerous hybrid mixture, safety was our highest priority.

• Based on a thorough explosion risk assessment, we selected equipment specifically designed for use in explosive atmospheres.

• Storage silos were equipped with an explosion relief system using decompression panels.

• To completely eliminate the oxidizer (oxygen from the air) required for a dust explosion, Wakro Sp. z o.o. installed a complete nitrogen inerting system. Oxygen sensors continuously monitor and maintain this inert gas atmosphere in all tanks.

By applying these innovative solutions and leveraging our proprietary patents, Wakro successfully delivered a safe, airtight, and highly precise installation that guarantees continuous production under the most demanding conditions.