Reactor Design

A) What is the type of reactor to be used?

We choose Plug Flow Reactor. This is because we have chosen to work on thermophilic temperature range for Single stage high solid (SSHS). Due to the viscosity, PFR were chosen. Besides that, PFR is the best option as it has no short circuit occurring unlike CSTR, due to no moving parts.

Single stage high solid (SSHS)

In dry system, the fermenting mass in the digester has a solid content which the main problem with the process is in transport and handling.

1)The pre-treatment step is much simpler with high solid because the system has a greater intolerance for the impurities.

2)Due to viscosity, plug flow reactors are used. The advantages are that it is technically simple and no mechanical devices need to be installed inside the reactor.

3)The reactor is also smaller because no water is added, so that the heat required in order maintaining the temperature in the digester at a constant level is less important.

B) What is the size of the reactor?

According to The Kroger Co, the optimum amount of organic waste produce per day is 150 tons. So, the size of reactor required is 2200 -3500m³ with 10-12m in height and 180-320m² of area based on table .

But our project is based on lab scale opearation , therefore:

C) Operating temperature and pressure?

Since we chosen thermophilic temperature range of process, so the operating temperature is 50-65°C, usually 55°C with retention time of from 12-14days.

And the operating pressure will be the atmospheric pressure.

D) Does it require any heating/cooling? How do you provide that?

Yes. It does require both heating and cooling processes. Heating system is a critical part for of the anaerobic digester. It need heating process to heat the waste, because it is a legal requirement for the digestate to be sanitised, in some cases this requires heating the waste to 70°C for an hour. Besides that the heating pipes in which hot water circulates must be able to heat up all the material entering the digester to 95°F and to resist corrosion from manure. Once the biogas is produced, it is sent to the conditioning unit for cooling purpose in order to compress the gas and remove the moisture for further energy production.

E) Mechanical Drawing

F) Costing

We must consider the suitability of the material for digestion of the vegetable waste as well as the compatibility of the material with the process environment. Carbon steel is chosen for the design of the anaerobic digestion because this does not need high specification of expensive material. It also supports thermophilic temperature ranges at ambient pressure.

The costing for reactor is based on the cost correlation method of reactors (Douglas, 1988).

Where M&S= Ratio indices= 1615

D= Reactor diameter, ft= 13.04ft

H= Height, ft= 22.80 ft

Fm= Material factor (Carbon steel)= 1.15

Fp= Pressure factor= 1.50

Fc= Correction factor = Fm Fp=1.725

Thus,

Installation cost = $ 40,470.62

Purchase cost = $ 20,400.13

Total cost = Installation cost + Purchase cost

= ($ 40, 470.62 + $ 20,400.13)

= $ 60 ,870.75

Since ($1 = RM 4.00)

Therefore, the total cost of the design is RM 243483.00