Chlorine Dioxide Technologies

Chemical Systems & Services

To assist pulp mills worldwide, ERCO Worldwide offers the following services for installations of chlorine dioxide, sodium chlorate and bleach chemical preparation facilities.

  • Engineering design
  • Equipment selection and procurement
  • Construction assistance
  • Plant and equipment commissioning
  • Operator training
  • Bleach plant audits and optimization
  • Safety audits and hazard analysis
  • Spare parts supply and service
  • Saltcake integration studies

ERCO® R –Series ClO2 Processes

are in service in over 100 pulp mills around the world. Each process plant is supplied with guarantees of production capacity, product quality and chemical efficiency.


The R3 was developed to meet the needs for reduced sulfur by-products from earlier chlorine dioxide processes. The R3 utilizes sodium chlorate, sulfuric acid, and sodium chloride (reducing agent) to produce chlorine dioxide, sodium sulfate (crystal co-product) and a chlorine co-product (as chlorine water or hypochlorite).


The R3H, in which part of the sulfuric acid and all or part of the sodium chloride is replaced by hydrochloric acid in order to achieve a balance in the production and recovery of sodium sulfate required by the mill.


The R5 was developed for mills that did not require any sodium sulfate co-product. The process utilizes hydrochloric acid and sodium chlorate to produce chlorine dioxide, chlorine and a solid sodium chloride co-product.


The R6 ClO2 plant is an R5 integrated with a sodium chlorate and hydrochloric acid plant, such that the only raw materials are electricity and chlorine.


In the R7, the by-product chlorine is reacted with sulfur dioxide, forming a mixture of sulfuric and hydrochloric acids, which is then re-used in the generator to eliminate chlorine by-product and achieve a reduction in the amount of sodium sulfate produced.


The R8 chlorine dioxide process utilizes methanol as the reducing agent to produce ClO2. No by-product chlorine is formed and co-product sulfate is less than with an R3 process.


This process features electrolysis of all or part of the salt cake from the chlorine dioxide process. The acidic solution produced in the electrolysis cells, can be recycled back to the chlorine dioxide process, or used elsewhere in the mill, thus reducing the mill’s acid requirements. The electrolysis cells also produce a co-product of sodium hydroxide that can be used within the mill.


The acidic by-product saltcake (sodium sesquisulfate) from the R8 process is converted to sodium sulfate. The acidic stream from the R10 is returned to the R8 process to reduce the acid requirement and the amount of saltcake co-product by about 24%.


The R11 chlorine dioxide process utilizes hydrogen peroxide as the reducing agent. No by-product chlorine is formed. When a catalyst is employed, sodium sulfate is produced; if a catalyst is not used (high acidity) then sodium sesquisulfate is produced.

ERCO R101®

The ERCO R101 is a small single chemical electro-chemical generator that produces a pure chlorine dioxide solution by passing chlorine dioxide gas through a gas transfer membrane into a receiving stream.


Electrolysis is used to convert part of the sodium chlorate feed stream of the R8 or the R11 process to chloric acid. The sulfuric acid consumption and the by-product sulfate production are reduced proportionately. Sodium hydroxide is produced as a by-product.


Crystal sodium chlorate from the generator and make-up sodium chlorate are passed through electrolysis cells to produce chloric acid to replace the sulfuric acid feed to the R8 and R11 processes. Only sodium hydroxide is produced as a by-product, thus eliminating sulfate by-products.


The ERCO CRP Chloride Removal Process was designed to improve recovery boiler operation and decrease boiler plugging. The CRP selectively removes chloride and potassium from recovery boiler precipitator ash, returning purified sodium sulfate crystals to the recovery cycle. With lower levels of chloride and potassium in the ash, the boiler can operate at higher temperatures with significantly decreased fouling. Commercial installations of the CRP have all shown that boiler reliability is increased due to the need for fewer shut-downs, fewer chill-and-blows, and fewer water washes.

Process Flexibility

The same basic process equipment can be utilized by most of the ERCO R-Series Processes to produce chlorine dioxide.