Case study in a chemical industrial company

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1. Type

Case study


2. Industry Sector

Chemical industry


3. Company’s description

The study was carried out in a super plasticizer production company. The main product is poly sulfonated naphthalene formaldehyde with a produced amount of 30.000 tons of liquid per year. It was tried to find options for pollution prevention measures and waste minimization. The measures should result in

  • Environmental improvements
  • Financial savings
  • Control of liquid and solid waste
  • Benefits from wasted materials


4. Process description


Two different kinds of waste are generated:

  • Liquid waste (40 m3/day)
It is discharged without any treatment into a pond within the vicinity of the company and then to the public sewage network.


  • Semi-solid waste (15 t/day)
It is produced in the filter press and is transported daily by a truck to a dumping site.


The chemicals used in procedure are hazardous and have serious effects on the environment and on the health of workers. The generated wastewater is very difficult to treat either biologically and chemically, because the contained organic constituents are hardly biogradable.


CP chem.ind. flowsheet.JPG

Figure 1: Processes and sources of waste in the company


5. Assessment of Cleaner Production


The methodology consists of different phases:

1. Industrial audit for the existing situation in the company.
2. Check on resource utilization (water and energy) and to recognize major sources of waste and emission.
3.Description of existing environmental situation in the company.
4. Quantitative and qualitative determination of solid and liquid wastes.
5. Studying the different approaches for pollution prevention and waste minimization in the company and suggesting possible alternative remedial integrated schemes including the in-process, or in-plant modifications.
6.Technical and economical cost benefits analysis.
7.Preparation of the preliminary engineering design.
8.Preparation of the tender documents of the proposed solutions.
9.Implementation of the proposed solutions.


Wastewater collection and analysis

For a period of two months the quality and quantity of the end-of-pipe was measured and analyzed.


Semi-solid waste collection and analysis

The sludge cake resulted from the filtration was analysed for sulphate, sodium and calcium ion and water content.


Utilization of the residual product from the semi-solid cake

The recovery of retained product in the cake happens by washing the cake intensively at ambient temperature. The resulted slurry was filtered and centrifuged.


6. Results


1. Recycling of retained water in filter press


Existing situation

The water flows out when the pressing pressure is released. The water consumption is 2 m3/shift or 6 m3/day. The wastewater is discharged to the floor under the filter press and then to the wastewater collection pond. The water contains very toxic and hazardous chemicals and increases the pollution load in the wastewater stream.


Proposal measures

Two mobile collection containers were installed to avoid spreading on the floor. Additionally it was proposed to raise the filter press elevation for proper collection of water and cake. The collectors are equipped with drain pipes ended by coupling. The water is pumped to recycling tanks and then to recycling vessel.


Savings

0.75 t of product per day OR 289.08 t per year


2. Recycling of washing water of reaction vessels (reactors)


Existing situation

Each of the existing five reactors is washed by 15 m3 of water every 45 days. So the total consumption is calculated with 75 m3/45 days. The washing water containing raw material and pieces of final product represents an environmental problem.


Proposal measures

Instead of disposal the washing water on the floor it is recycled by discharging to a special collection tank (Volume: 15 m3). A still existing scrubber tank (Volume: 12 m3) is refilled by “make-up” water twice per day. The collection tank is used as storage tank to provide the scrubber tank by the make- up water to use it for washing the reactors.


Savings

50 m3/month OR 1050 m3/year


3. Closed circuit cooling system for the high pressure pump


Existing situation

A high pressure pump is used for spray drying of the product to change its status from liquid to powder. The water rate is 24 m3 per day. The cooling process is an open cycle and the cooling water is directly discharged to the pond.


Proposal measures

A chiller closed cooling system is used instead of the open one.


Savings

24 m3 water/day OR 15.120 m3/year

Reduction of final hydraulic load of the wastewater: 40%


4. Minimization of leakage of raw materials, products and water


Existing situation

The raw material/product/feeding pumps suffer from leakage. The lost material is firstly discharged to the drain and then to the pond. Also the pump in spray dryers suffers from clean water leakage. The water contains chemicals from the processes and from the final product which are toxic.


Proposal measures

A rethinking of housekeeping and a change in workers behaviour were suggested. Furthermore existing pumps need proper maintenance and rehabilitation.


Savings

In product: 0.016 ton/day,

In raw material: 0.008 ton/day,

Reduction of water quantity: 2 m3/day,

Total benefits: L.E 43070/year.


5. Utilization of retained product from the semi-solid waste


Existing situation

A cake is produced from the separation of the final product from the mother liquor. For the process a filter press is used and the total produced amount of cake is 15 tons per day. It is later daily discharged to a dumping site. The leachate from washing the cake contains 21% of the final product and a high concentration of calcium salt which represents the residual solid.


Proposal measures

To utilize the retained product in cake a special type of filter press is used for the separation of product and solids. The produced salt is more than 45% of the total weight of separated solid and can be solved as by-product.


Savings

In products: 3.15 t/day OR 4 171.19 t/year

In salts: 6 t/day (is sold as by product).


6. Economical savings


Improvement measures Cost L.E/year Benefits L.E/year Payback period days
Recycling of retained water in filter press
Capital cost 40.000 289.000 56
Annual operation and 30.000
maintenance cost
Recycling of washing water of reaction vessels (reactors)
Capital cost
Annual operation and 50.000 1.050 -
maintenance cost 30.000
Closed circuit cooling system for the high-pressure pump
Capital cost 150.00 15.120 -
Annual operation and 12.000
maintenance cost
Leakage of raw material, products, and water
Capital cost 6.000 43.070 115
Annual operation and 24.000
maintenance cost
Utilization of the residual product from the solid waste (cake)
Capital cost 700.000 4.171.950 61.5
Annual operation and 12.000
maintenance cost
Total capital cost 946.000 4.412.270 78.25
Total annual operation and maintenance costs 108.000


Source: Sohair I. Abou-Elela , Hesham Abdel Haleem , Enas Abou-Taleb , Hanan S. Ibrahim: Application of cleaner production technology in Chemical Industry: a near zero emission, published in Journal of Cleaner Production Vol. 15 (2007)


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