Subcritical water technology opens a new way to the future of industrial waste recycling business

(Industrial Waste Close-up 2008.10)

REMATEC Corp. Sakai SC Factory

Outline of REMATEC Corp.

Foundation : November, 1974
Location of head office: 11-1 Jizouhama-machi Kishiwada city, Osaka
URL : http://www.rematec.co.jp
Outline of Sakai SC Factory
Location : 4-2-4 Chikuko Shin-machi Nishi-ku Sakai city, Osaka Pref.
Types of facility: Subcritical water reaction treatment plant 70 t/day (24h)
Weak acid liberation reaction disposal plant 7 t/day (24h)
Employees: 20 persons (Operating division: 11 persons, Research division 9 persons (including analysts)
Licensed waste: Industrial waste (sludge, waste oil, waste acid, waste alkali, waste wood, waste plastics, animal and plant residue, livestock excreta)
Specially controlled industrial waste (sludge, waste oil, waste acid, waste alkali
Site area: 10,420 m2

Introduction

REMATEC Corp. is known as the company which recycles wastes into reclaiming fuel (RF), and sells it to cement plants and others.

REMATEC had an interest in “Study on waste recycling with subcritical water reaction field” carried out by professor Yoshida at Osaka Prefecture University as a new business following RF business; under his advice, REMATEC has worked for the development of a practical application, and succeeded in its commercialization as a part of Osaka eco-town project.

This time, JW visited Sakai SC Factory located in Sakai city, Osaka prefecture and interviewed Mr. Tanaka, executive director (now vice president) about SC (waste recycling with a subcritical water reaction field) business concerning its development history, technology content, present business state, and challenges for the future.

SC technology

When raise the temperature and pressure of water up to 374℃/22MPa (about 220 times of atmospheric pressure), it becomes a state where it is neither water (liquid) nor water vapor (gas) (Figure 1). SC technology is to perform recycling of various wastes using the behaviors of the particular water state called “subcritical state” lying marginally beneath the critical point.

Phase diagram of water
Figure 1. Phase diagram of water

In the case of dechlorination/recycling of chlorinated organic solvent, waste solvent and sodium hydroxide (NaOH) together are put in a subcritical water reaction field, and chlorine (Cl) is separated from the solvent, and then salt (NaCl) is recovered as reaction product. Meanwhile, dechlorinated waste solvent is recovered as alcohol and organic acid depending on the degree of decomposition.

Factory

Based on the above basic technology, REMATEC constructed a commercial factory in Sakai city, and started its operation in December, 2006. A view of recycling plant is shown in Photo 1 and the process flow of the plant is shown in Figure 2.

A view of the recycling plant
Photo 1. A view of the recycling plant

A flow of subcritical water treatment
Figure 2. A flow of subcritical water treatment

In the commercial operation of the factory, special efforts were and are made in safety measures. More specifically, a safety assessment approach related to a chemical plant which were adopted by PCB disposal facilities was implemented by applying such approach to the designing, construction and operation based on the guideline provided by Health, Labor and Welfare Ministry; as a result, high evaluation by the fire department of Sakai city was obtained.

Operation

As for the operation of the plant, recycling processes currently REMATEC puts most of its efforts into are as follows:

  1. Dechlorination recycling process of organochlorine solvent waste: Organochlorine solvent waste is treated by subcritical water, and then alcohol, organic acid, and natrium chloride are recovered as raw materials for industrial use.
  2. Production process of biodiesel: Animal and plant grease production residue is treated by subcritical water, and then biodiesel and crude glycerin for industrial use are recovered.

Reside comes out of these processes are recycled at a RF plant as raw materials for an alternate fuel of coal to be used at a cement plant, etc. Almost 100% recycling is achieved through the thoroughgoing recovery of useful materials and the reuse of residue.

As pointed out above, as for the operation, efforts are made to maximize the recovery of useful materials; for this purpose, preparing a best formulated prescription based on sufficient sample analyses and tests is the key for successful treatment. Maximum recovery of useful materials is an important subject to be addressed in order to cope with a recent escalating fuel price.

Challenges for the future

SC business opens a new way for recycling of wastes such as chlorinated organic solvent which have been and are disposed by mainly incineration. It is REMATEC’s prime task to expand SC business based on this competitive edge.

Meanwhile, as for the expansion of application of SC technology, the application to the methane fermentation of food waste is promoted. SC technology is used for a pretreatment of methane fermentation. This makes it possible to downsize a methane fermenting tub, to cut down fermentation time, to improve digestive efficiency and to reduce the volume of effluent treatment. A methane fermentation plant using SC technology may be capable of solving odor troubles along with the improvement of various functions. It is thus expected to be suitable for the use in an urban area.

A corporate model aimed by REMATEC is a “Zero-emission engineering company” placing stand-alone technology as a core business driving force. It is expect that SC business would grow to a new core business driving force of REMATEC and contribute in the creation of a sound material-cycle society.

(Reported by Ozaki, JW)