Pyrolysis based sanitary napkins incinerator Version 3.1

Background :

                              Disposal of used sanitary pad & similar kind of medical waste has been a very common problem. In general the used napkins are thrown to dustbins or flush in to t he drain. The open disposal of soiled pads not recommended due to hygiene issues. Disposal problem is difficult due to use of gel forming polymers used in modern day’s pads. It has also a taboo factor attached to further increasing complicity of disposal. Incineration of medical waste is one of the possible ways to dispose sanitary pads.

Incineration Process –

                 Incineration is a thermal waste treatment process that involves the combustion of organic substances contained in waste materials. Incineration of waste materials converts the waste into ash, flue gas and heat.

Problems with Direct Incineration –

                               The pads are wet during disposal, so during incineration the amount of smoke observed from exhaust/ chimney is too much and the flue gases generated are pollutants. So direct incineration of soiled pads is not a good waste disposal method.

To solve this problem we use pyrolysis process for soiled pad disposal;

Pyrolysis Process –

                     Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere. The products of pyrolysis are combustible gases. So, by complete combustion of those gases the problem in direct incineration can solve.

On the principle of pyrolysis Incinerator is deigned and developed in Vigyan Ashram.

Existing Version –

                      An incineration device has been developed that uses pyrolysis to decompose sanitary napkins into hydrocarbon vapours and combustible gases along with some non-combustible gases and char. These vapours and gases are made to pass over high temperature electric coils (>5000C) where they auto-ignite in the presence of oxygen. The heat from the flames partially drives the pyrolysis of remaining sanitary pads. Combustion conditions that result in a transparent flue gas exiting from the chimney.

Limitations with Existing Version –

  1. Electrical heating coil is given at below the pyrolysis chamber which is used to burn the gases from pyrolysis, and the heat generated is utilized to heat the pyrolysis chamber. During this process the heating coil get fused due to uncontrolled temperature. 
  2. Uneven heating of pyrolysis chamber due to improper location of the heating coil.

Proposed Design –

                    This system will be based on drying & pyrolysis process to decompose sanitary napkins into combustible gases and char. This system will firstly prefer for drying of sanitary pad at 1000C-1200C temperature. Then pyrolysis process will happen to decompose dried sanitary napkins at 4500C-5000C temperature, hence generates combustible gases & char. These generated combustible gases also utilize for heating reactor through burner. But initial heating would be done by the electrical heaters. In this system we also go for directly pyrolysis to decompose waste plastic into combustible gases & char.

Design Process

1. Ideation –

In brain storming with DIC Fellows and Dr. Arun Dixit following considerations were finalized –  

  1. Capacity of the Incinerator – 1 to 20 pads
  2. Weight of dry pad – 7 to 10 gm.
  3. Weight of wet pad – 90 % to 93 % of weight of dry pad.
  4. Basic Dimensions
  5. Operating Temperature Range
  6. Heaters
  7. Chimney and exhaust system
  8. Air Supply for Drying phase
  9. Apparatus Cleaning and Handling 

By considering the above points 1st 3D model done as following ;

Model A


Model A: 1st 3D CAD Model (Full View of pyrolysis chamber)


Model A: Section View

  • Model A is with SS container (220mm height 180mm dia. And asbestos as a gasket material which is used in IC engines. The upper lead and incinerator male reactor will get attached with each other by nut and bolt arrangement similar to autoclave.
  • Model A has ceramic heaters on bottom 1/3rd area of periphery with air blowing in order to push out vapours generated. First drying phase will operate in 110130 degrees.
  • The real incineration will happen below pyrolysis chamber same as V1 pyrolysis model (subir sir).

Model B

following points raised in further discussions;

  • How much heat will generate by incineration of pyrolysis gases. The weight of polymer is close to 140 grams or 20*7 grams. We guessed the heat generation equivalent to incineration of 140 gm of cotton. This heat is negligible not very substantial hence we decided a trap between heat utilization and ease of manufacturing. The second model be hence proposed with incineration of paralytic gases at the end of chimney.
  • Will there be a channelization of air and will air flow accelerate or disaccelerate drying. Knowing the structure of substrate chalking was 100% assure which will result in losses of heat without assisting real dry. Hence it was decided to remove the air blower and suction in model B.

With above considerations 3D modls made as following;

CS view 1.JPG

Cross Sectional View of Model B

The following topics also raised during discussions and brainstorming with Mr. Dasnurakar ;

  • Possible channelization of hot air.
  • Knowing the real life practice and random shape and density of soil pad it was thought that channelization of hot air is almost certain. This will result into loss of hot air without effecting drying.
  • On the other hand slow heating through insulated material will lead to less consumption of electricity it was hence decided to remove fan to generate air current. As a result new model proposed it got simplified the next point discuss was incineration of pyrolytic gases.
  • . If we incinerate pyloric gases beneath the pyrolysis chamber we will be able to use heat generated.

The cal. To get the saving of electricity by burning of pyrolytic gases is as follows:

  • We assume that the calorific value of sanitary napkin pad is equivalent to cotton which in reality will be slit lower. 8gms of cotton per pad will generate 12.8 kcal assuming 1600kcal/kg as calculated value of pure cotton. 2kw heater can generate same amount of energy in 26.7sec. Lead into next consumption of 0.14*10-3 units. Which is equivalent to 1.5paise assuming the unit rate to be 10rupees. That means 75paise saving per batch of 50 pads.
  • This was thought to be too low advantage for the capital cost investment. This gave us clear answer that we can incinerate the pyrolytic gas at top of chimney.

2. Material Selection (MOC) –

Following are the options of the materials for the pyrolysis chamber; 

  1. Ceramic
  2. SS 316L
  3. MS (CRCA) sheet
  • Inside Chamber Dimensions are, 
    Inner Diameter – 18.2 cm 
    Height – 21.7 cm 
    Perimeter is 58 cm

So it requires 58.0*21.7 cm sheet

For bottom blank 18.6 cm dia. Sheet For top flange Inner Dia. 18.2 cm , Outer Dia. 31.4 cm 
Total sheet required = 4*1 ft.

  • Outer Shell 
    Inner Diameter – 26.5 cm 
    Height – 26.3 cm 
    Perimeter – 83.8 cm 
    So, Sheet Size will be 83.8 * 26.3 cm 
    For bottom Blank 27 cm dia. Sheet 
    For top flange Inner Dia. 26.5 cm, Outer Dia. 29 cm 
    Total Sheet required = 5 * 1 ft.
  • Lid 
    2 Plates of dia.31.4 
    Sheet Required = 2*1 ft 
    # By considering above dimensions Sheet of around 12 sq. ft. is required. 
    # Thickness of material is 2 mm.

Considering various factors related to heat transfer and thermal cycles during operation of incinerator SS 316 sheet was considered as material of incinerator.

By checking availability and costing of SS 316 it was decided to use MS CRCA sheet of 2 mm thickness for the prototype.

3. Detailed Drawings and CAD Models –

As shown in above conceptual CAD model the assembly is made of three main systems, which ar;

  1. Inside Chamber (Pyrolysis Chamber)
  2. Outer Shell
  3. Lid and chimney
  • Inside (Pyrolysis) Chamber

This is the main chamber which will be the air tight vessel with the requirement of avoiding air coming into the chamber which will led to disturbance in pyrolysis process.

  1. Inner Shell 

It is cylindrical part made of MS CRCA 2mm thick sheet.

Inner shell
Inner Shell 3D Model
Inner Shell.JPG
Inner Shell Drafting

2. Inner Shell Bottom Blank

This part is the bottom for enclosing the inner shell and make it air tight from bottom side.

Inner Bottom Blank
Inner Shell Bottom Blank

3. Inner Shell Flange –

This flange has to weld with the cylindrical inner shell and will be covered by gasket from top to make air tight joint between lid surface and inner shell. It has also provision of holders to tight the lid using wing nuts.

Inner Shell Flange.JPG
Inner Shell Top Flange
Inner Shell Top Flange Drafting

4. Wing Nut Mount –

This mount will weld to the inner shell top flange to hold the wing nut.

Wing Nut Mount.JPG
Wing Nut Mount
  • Outer Chamber –
  1. Outer Shell –

This is MS CRCA 2 mm thickness sheet rolled vessel for holding the complete assembly of inner shell by making gap between both and filled with glass wool to prevent heat transfer to outside surface.

Outer Shell.JPG
Outer Shell 3D
Outer Shell.JPG
Outer Shell Drafting

2. Outer Shell Bottom Blank –

This is for enclosing the outer shell from bottom side.

Outer Shell bottom.JPG
Outer Shell Bottom Blank
Bottom Drafting.JPG
Outer Shell Bottom Blank Drafting

3. Outer Chamber Complete Assembly –

Outer Chamber.JPG
Outer Chamber Complete Assembly 
  • Lid –

Lid will hold complete pressure building inside the pyrolysis chamber. This will made up of two flat plates joined by round plate and by maintaining gap between the plates filled with glass wool. Also provided handle for handling and wing nut fitting gaps required during locking of the vessel.

  1. Lid Round Plate –
Lid Round Plate.JPG
Lid Round Plate

2. Lid Top Plate –

Lid top.JPG
Lid Top Plate
Lid Top Plate Drafting.JPG
Lid Top Plate Drafting

3. Lid Wing Nut Mount –

Lid Wing Nut Mount.JPG
Lid Wing Nut Mount

4. Lid Assembly –

Lid Assembly.JPG
Lid Assembly
  • Incinerator Complete Assembly –

Following is the complete CAD assembly of the pyrolysis based sanitary napkin incinerator. It is showing inside pyrolysis chamber, lid and outside chamber.

Inc Complete Assembly.JPG
Incinerator Full Assembly 3D CAD Model


  • CRCA Sheet LASER Cutting –

The MS CRCA Sheets cutting using LASER cutting according to the design and .DXF files of the same. The material cutting work outsource from Ms. Kakade LASER Pune, since the CNC plasma cutting machine in Vigyan Ashram is under maintenance.

WhatsApp Image 2018-10-15 at 1.25.17 PM.jpeg
LASER Cutting
WhatsApp Image 2018-10-15 at 1.25.16 PM.jpeg
LASER Cutting
  • Sheet Rolling –

For making inner pyrolysis chamber and outer chamber cylinderical, rolling machine used and rolling done.

  • Welding – 

Welding of the joints after rolling done. Chimney pipe also welded to the inner chamber. Flanges at the top of the inner chamber welded and the chamber is tested for leakage checking by filling water. The chmber is found leakproof.Outer Chamber also Welded after checking the sizes of heaters. Heater Mountings welded to the outer surface of inner chamber.  Lid is fabricated by welding the wing nut mountings and handle. Insulation of Glass wool between two chambers is filled. Gasket is installed on top flange.

Inner Chamber with Gasket and wing nut mount and wing nut

The chamber is tested for its leak proof welding by filling water inside and kept for 3 hours. No leakage observed during the test.

  • Thermocouple Mounting –

The J-Type Thermocouple is mounted at the bottom Side to sense the temperature inside the chambermand also at the outer surface of inner chamber to sense the inner chamber surface temperature;

Inner Chamber with Thermocouple
  • Heaters Mounting –

Heater details:

Heater type – Ceramic IR heaters (Curved type)

Specifications – 122mm*60mm*500 Watt * 240 Volts AC

Image: Ceramic IR heater

Heaters are mounted on the 1/3 rd surface considering vertical height of the pyrolysis chamber outer surface.

Heaters Mounted

This heaters mounted using clamp made from MS CRCA 1.5 mm thick sheet. The clamp having u type notches to hold the heaters outer mounting part. The gap between two heaters is filled by glass wool.

Image: Heater mounting clamp

The front side surface of the IR ceramic heaters is in direct contact with the outside surface of pyrolysis chamber.

During Thermocouple Mounting

For mounting thermocouple sealant used to seal the minor gap which can be sustain up to 1000 degree Celsius.

  • Thermocouple – J type industrial
Image: J type Industrial thermocouple
  • Temperature Controller – Selec PTC 513
Image: Selec PTC513
  • Thermocouple and LCD display for Inner Chamber surface temperature –
  • Final Assembly

The final assembly of incinerator is demonstrated in following image. Chimney is attached permanently with leak proof welding to the pyrolysis chamber for carrying the combustible pyrolysis gases out for burning.

By considering calculations of calorific value we can get from the combustion of pyrolysis gases done which we found 10 % that of we required for pyrolysis chamber heating if we burn it beneath the pyrolysis chamber, along with this considering design complications it was finalized to burn the pyrolysis gases at the tail of chimney.

Image: Complete Assembly


Trials initiated for testing various parameters.

Idle trial of incinerator taken to understand temperature difference between outer surface or pyrolysis chamber wall and cnter point of the pyrolysis chamber.

Average difference of temperature throughout the trial observed in the range of 200° C to 250° C.

  • Trial 1 – Trial on wet cotton

Following are the observations from the trial taken on wet cotton. To make the cotton wet water is added and trial taken.

Trial 1                                    Date – 30/11/2018  Trial on Wet CottonTotal heaters run time = 10 min. 30 sec.All next 6 trials heaters run time 229 min. = 3 hrs. 49 min.
Inside Temperature (Degree Celsius)Surface TemperatureTimeTime (Minutes)Set TemperatureHeaters StatusHeaters Run timeComment
285416:45090OnDrying Started
8038516:50590OnMoist Fumes Started
8239616:50590OnMoist Fumes
8540416:50590OnMoist Fumes
8841116:50590On16:50 -16:45Moist Fumes
9041816:50590OffMoist Fumes
9443016:50590OffMoist Fumes
9543916:50590OffMoist Fumes
9844616:50590OffMoist Fumes
10145116:50590OffMoist Fumes
10445816:50590OffMoist Fumes
10646316:50590OffMoist Fumes
10846916:50590OffMoist Fumes
11147316:51690OffMoist Fumes
11548016:51690OffMoist Fumes
12048616:51690OffMoist Fumes
12249316:51690OffMoist Fumes
12749716:51690OffMoist Fumes
13150116:51690OffMoist Fumes
13250216:51690OffMoist Fumes
13550416:51690OffMoist Fumes
13750616:51690OffMoist Fumes
14050716:51690OffMoist Fumes
14150816:51690OffMoist Fumes
14250916:52790OffMoist Fumes
14551016:52790OffMoist Fumes
14751016:52790OffMoist Fumes
15251016:52790OffMoist Fumes
15551016:52790OffMoist Fumes
15650916:52790OffMoist Fumes
15850916:52790OffMoist Fumes
16050816:53890OffMoist Fumes
16150616:53890OffMoist Fumes
16450616:53890OffMoist Fumes
16650216:53890OffMoist Fumes
16750216:53890OffMoist Fumes
16849916:53890OffMoist Fumes
16949816:53890OffMoist Fumes
17049716:53890OffMoist Fumes
17149416:53890OffMoist Fumes
17249316:54990OffMoist Fumes
17548316:54990OffMoist Fumes
17548116:54990OffMoist Fumes
17747716:54990OffMoist Fumes
17747716:54990OffMoist Fumes
17847516:54990OffMoist Fumes
17847216:54990OffMoist Fumes
17846916:551090OffMoist Fumes
17946516:551090OffMoist Fumes
18045016:5611200OnMoist Fumes
18245216:5611200OnMoist Fumes
18345816:5712200OnMoist Fumes
18446416:5712200OnMoist Fumes
18747516:5712200OnMoist Fumes
19249616:5712200OnMoist Fumes
19450616:5712200OnMoist Fumes
196514.516:5712200On16:57 – 16:56Moist Fumes
20052316:5712200OffMoist Fumes
20253116:5712200OffMoist Fumes
20453716:5712200OffMoist Fumes
20954716:5712200OffMoist Fumes
21255316:5712200OffMoist Fumes
21455716:5712200OffMoist Fumes
21756116:5813200OffMoist Fumes
22356916:5813200OffMoist Fumes
22557216:5914200OffMoist Fumes
22957516:5914200OffMoist Fumes
23157716:5914200OffMoist Fumes
23858116:5914200OffMoist Fumes
24158316:5914200OffMoist Fumes
24358316:5914200OffMoist Fumes
24558416:5914200OffMoist Fumes
24958417:0015200OffMoist Fumes Stopped
25358317:0015200OffDry Gases
25458217:0015200OffDry Gases
25558217:0015200OffDry Gases
25958017:0015200OffDry Gases
26057917:0015200OffBreaking Flame Started
29862217:0419300On17:04 -17:03
41877717:1025450On17:10 – 17:07:03
44873617:2035450On17:20 – 17:19
38556317:3742350OffGases Stopped Coming out

Following is the graph showing the Inside temperature and outside surface temperature of pyrolysis chamber with respect to time.

Trial 1
Image: Time Vs. Temperature curves on Inside chamber (Pyrolysis Chamber) and outside chamber

Trial outcomes-

  1. In this trial drying and pyrolysis observed also flame generated at the tail of chimney where orifice of 6 mm diameter installed by using candle as external source to start combustion of the pyrolysis gases.
  2. This trial was also performed to understand the temperature ranges and heater performance.
  3. The pyrolysis chamber also tested with no leakage found. This trial was aimed at testing the prototype system only.
  • Trial 2 – Trial on 3 Dry Pads

Following is the result and observations table along with the comments.

Trial 2      Dry Pads                                                                  Date – 15/12/2018   and  16/12/2018                                 Dry Pads                                                               No. of Pads- 3                                                      Weight of Pads      (With Cover)                             ( Before Incineration)                              1. Sample S1 – 6.30 gms                 2. Sample S2 – 6.30 gms                 3. Sample S3 – 6.30 gms                         Weight of Pads (After Incineration) 1. S1 – 1.38 gms         2. S2 – 1.44 gms          3. S3 – 1.38 gms                                                            Total Trial Time – 121 min. Total Heater On Time – 20 min. 30 sec.
Inside ChamberSurface TemperatureTimeOuter chamber TemperatureSet TemperaturesHeaters StatusCommentsAvg
5633611:1928.5250OnGas Started196
33070611:2432.7250OffYellowish Red Flame started518
26039011:4563.1250OffBluish Flame Burning (Breaking)325
25137011:48250OffGases flow and Flame Contnd.310.5
27744511:56250OffGases flow and Flame Breaking          Valve Closed361
27042411:58250OffValve Opened                                              Slow Gas flow347
26139612:01250OffGray Color gases Coming                                 ( Breaking Flow)328.5
25337712:04250OffSame as above315
24836812:05250OnSame as above308
25241512:06250OffSame as above333.5
26445112:07250OffSame as above357.5
27746912:09250OffSame as above373
28545512:11250OffSame as above370
27242212:15250OffValve Closed347
26540512:17250OffValve Opened                                              Breaking Gas flow335
24936612:22250OffIncreased Gases density307.5
25140812:24250OffContinuos Gas flow with high velocity visual Observations329.5
28046612:26250OffIncreased Gases density373
26540112:34250OffBlackish gray Gases with breaking Flow333
25137012:39250OffReduced gas flow310.5
25141112:41250OffVery low dense gas flow with high velocity331
28246012:44250OffIncreased Gases flow rate and medium dense371
28850212:47350OnIncreased gas flow and velocity, more continuos395
41370812:51350OffGrayeish white flame burning contin.560.5
41068512:53350OffValve Closed547.5
39564612:55350OffValve opened, very slow gas coming520.5
36356413:00450OnGases stopped463.5
46975613:13450OnContinuos Flame and condensed liquid at chimney612.5

Following is the graph of temperatures with respect to time.

Trial 2
Image: Time Vs. Temperature curves on Inside chamber (Pyrolysis Chamber) and outside chamber

Trial Outcomes –

  1. The average temperature difference observed of 150 degree Celsius during the trial between pyrolysis chamber surface and center.
  2. Pyrolysis temperature range testing is started for dry sanitary pads which will be reference for further trials.
  3. Burning of gases and flame observed during the trials.
  4. It is confirmed that pyrolysis is happening with the 3 dry pads of weight 18.90 gm.
  5. The remaining material as ash is 4.2 gm.
  6. Next trial required to perform for checking electricity consumption for complete pyrolysis of dry pads.
  • Trial 3 – Trial on 3 dry pads
Trial 3      Dry Pads                                                                 Date – 17/12/2018                                                        Pads – whisper ultra dry                                                                      No. of Pads- 3                                                      Weight of Pads      (With Cover)                             ( Before Incineration)                              1. Sample S1 – 5.71 gm.                 2. Sample S2 – 5.75 gm.                 3. Sample S3 – 5.75 gm.                     Total Weight – 17.21 gm.                                     Weight of Pads         (After Incineration)         1. S1 – 0.85 gm.                  2. S2 – 0.78 gm.                  3. S3 – 0.77 gm.                  Total Weight – 2.41 gm.Total Heater Run Time – 14 min. 45 sec.
Inside ChamberSurface TemperatureTime 1TimeSet TemperaturesHeaters StatusComments
2326013:00450OnValve closed
54301413:04450OnValve Open , Gas Started coming out
246660713:07450OnGases coming slowly
300722813:08450OnFlame Started, Bluish Fame
379803913:09450OnGases and flame contnd. Without condensation
4998961213:12450OffGases slow down, flame braking
4718171413:14450OffBreaked gas flow
4507551613:16450OnValve closed
4757802013:20450OffValve open, flame started, Yellowish green flame, Breaking gas flow
4517392513:25450OffGas flow slightly increased, flame proppogating
4777642713:27450OffGases coming slowly, breaked flow, flame starting
4557083013:30450OffGas slow down
4496953113:31450OnGases very much slow down
3213:32450No ElectricityFlame burning, slow down gases burning flame
3313:33450No Electricity
3713:37450No Electricity
4113:41450No ElectricityGases coming very slow,too slow, burning by candle
4713:47450No ElectricityVery slow and negligible gas flow

Following is the graph of temperatures with respect to time.

Trial 3.
Image: Time Vs. Temperature curves on Inside chamber (Pyrolysis Chamber) and outside chamber

Trial Outcomes –

  1. Heaters run time found 14 min. 45 sec. that is 1 kw
  2. Complete pyrolysis observed in this trial since the ash remained is 1/2 by weight as compared with previous trial.
  3. Next trial need to perform for increased no. of pads.
  • Trial 4 – Trial on 4 dry pads
Trial 4         Dry Pads                                                               Date – 02/01/2019                                            Dry Pads                                                               No. of Pads- 4                                                      Weight of Pads      (With Cover)                             ( Before Incineration)                              1. Sample S1 – 7.70 gms                 2. Sample S2 – 7.82 gms                 3. Sample S3 – 7.60 gms                 4. Sample S4 – 7.47 gms           Total Weight – 30.59 gms                                     Weight of Pads         (After Incineration)           Total Weight – 3.97 gms  Percentage residues – 12.9781 %Total heaters run time = 47 min.
Inside ChamberSurface TemperatureTime 1Set TemperaturesHeaters StatusCommentsHeatrs Run TimeTime
894609450OnGas satrted15:54
12054010450OnValve closed15:55
14657011450OnValve opened, gas coming, No flame15:56
22967115450OnLow flame starting16:00
27771818450OnFlame started, non contn. Gases, valve closed16:03
31676620450OnFlame contnd. Without external support16:05
42286226450OnCondensed liquid coming16:11
43387627450On16:12 – 15:4516:12
44889129450OffFlam braking16:14
45387330450OffGases braking, valve closed16:15
44986833450OffFlame contnd.16:18
44282836450OnFlame cutting16:21
44683738450OnVery low flame, gases16:23
45785139500OnFlame contnd.16:24 – 16:2116:24
50488449500OffFlame braking16:34
50888955550OnFlame contd. Braking after long time, Dark smoke after burning16:40 – 16:3516:40
55395160550OffGases and condensed liquid both burning16:45
54894163600OnFlame trying to sustain16:48
59199772600OnFlame cutting16:57 – 16:4616:57
74OffTrial Over16:59
Trial 4.JPG
Image: Time Vs. Temperature curves on Inside chamber (Pyrolysis Chamber) and outside chamber
Image: Trial on 4 Sanitary Pads
Image: Flame of pyrolysis gases
Image: Continuous flame

Trial Outcomes –

  1. Total heaters run time observed 47 min. is very high as compared with previous trials.
  2. Ash content is 12.97 %
  3. Further trial required to be perform for wet or soiled sanitary pads.
  • Trial 5 – Trial on 4 wet pads
Trial 5         Wet Pads                                                               Date – 04/01/2019                                             Wet Pads                                                               No. of Pads- 4                                                      Weight of Pads                                   ( Before Incineration)                              1. Sample S1 – 7.60 gms                 2. Sample S2 – 7.78 gms                 3. Sample S3 – 7.70 gms                 4. Sample S4 – 7.70 gms           Total Weight of Pads – 30.78 gms                                           Weight of Water Added (50 % by weight)                                                                                        1. In S1 – 7.60 gm.               2. In S2 – 7.70 gm.               3. In S3 – 7.85 gm.                4. In S4 – 8.28 gm.       Total Weight Of Water added – 31.43 gm.                                                                Total heaters run time = 73 min.
TimeInside ChamberSurface TemperatureTime 1Set TemperaturesHeaters StatusCommentsHeaters Run time
9:062125050OnDrying started
9:12:30443876.550On9:12:30 – 9:0606 min. 30 sec.
9:4010133434110OnFumes started coming, moist
9:41:3010843235.5110On9:41:30 – 9:36:3005 min.
9:4412049938110OffMoist fumes(with droplets
9:4812343742110Offlow Condensation contd., most fumes also coming
9:5512833549110OffLow moisture, periodic condensation and exit of droplets
9:57:30:0012931951.5110Offlow vapours, low fumes
10:0513125759110OffDrying considerably over since no vapours, no fumes
10:1013838764500OnFumes started, very low and minor vapours
10:11:3015247365.5500OnFumes started, condensation also seen
10:13:3017655267.5500OnDense fumes
10:1621663570500Onlow vapours and heavy fumes
10:2031073074500OnBreaking flame with low vapours and condensation
10:24:3038781978.5500OnFlame breaking, condensation mix
10:2842986482500OnFlame started and contnd. With condensed liquid drops
10:34:3048492888.5500OnContnd. Flame and condensed droplets10:34:30 – 10:0631 min. 30 sec
10:37:3050293591.5500OffFlame contnd., no condensation
10:4150492295500OffBreaking flame.
10:42:3049890196.5500OnFlame breaking, condensation mix
10:44:1649589898.25600OnBreaking flame
10:46:3051392498.5600OnFlame contnd..
10:545761008106600OnFlame contnd.
10:565871023108600OnFlame braking
10:585881023110600Onvalve closed
11:005891023112650Onvalve opened, gas flow and flame breaking
11:065951023118650Onvery low gas flow
11:18492784130650OnVery low dense and breaked gas flow.11:18 – 10:42:3024 min 30 sec
Trial OverTrial Over.
Trial 5
Image: Time Vs. Temperature curves on Inside chamber (Pyrolysis Chamber) and outside chamber
Image: Wet pad
Image: Pads in loading cage

Trial Outcomes –

  1. In this trial both drying and pyrolysis observed. Pads made wet with same amount of water by weight.(31 gm. for 30.78 gm. weight of pads)
  2. Drying time observed 47 min. while pyrolysis and flame observed for 45 min.
  3. Heaters running time was 73 min. and energy consumption 5 kw for 4 wet pads disposal.
  4. From this trial we can conclude that INR 12.5 required for disposal of 1 soiled pad which is not economical or viable.
  5. Next trial required for increasing capacity and reducing cost per pad of disposal.
  6. Average temperature difference is 200 to 250 degree Celsius.
  7. After completing the drying process of soiled pads inside temperatures need to have in the range of 450 degree Celsius to 600 degree Celsius for complete pyrolysis.

Trial 6 – Trial on 7 wet pads

Trial 6         Wet Pads                                                               Date – 12/01/2019                                             Wet Pads                                                               No. of Pads- 7                                                      Weight of Pads                                   ( Before Incineration)                              1. Sample S1 – 6.80 gm.                 2. Sample S2 – 6.81 gm.                 3. Sample S3 – 6.52 gm.                 4. Sample S4 – 6.65 gm.                 5. Sample S5 – 6.95 gm.                 6. Sample S6 – 6.68 gm.                   7. Sample S7 – 6.73 gm.           Total Weight of Pads – 47.14 gm.                                           Weight of Water Added (50 % by weight)                                                                                        1. In S1 – 6.80 gm.               2. In S2 – 6.80 gm.               3. In S3 – 6.50 gm.                4. In S4 – 6.93 gm.            5. In S5 – 6.97 gm.             6. In S6 – 6.88 gm.             7. In S7 – 6.97 gm.      Total Weight Of Water added – 47.85 gm.                                                                 Weight After Incineration   – 7.6 gm.Total Heaters run time = 63 min. 35 sec.
TimeInside ChamberSurface TemperatureTime 1CommentsSet TemperaturesHeaters StatusCommentsHeaters run timeAverage
9:53:30424258.5Gas startedOnGas started233.5
9:555649010On9:55 – 9:4510 min.273
9:59:308446114.5Gases stoppedoffGases stopped272.5
10:01874531690on10:01 – 10:0001 min.270
10:029048517Gases coming without moistureoffGases coming without moisture287.5
10:0810741223No gas, no moistureoffNo gas, no moisture259.5
10:2511037540Gas comingonGas coming242.5
10:2711748842Gases flow increasedonGases flow increased10:27 – 10:2106 min.302.5
10:3013251045Gases fom chimney mid hole and droplets from downside tipoffGases fom chimney mid hole and droplets from downside tip321
10:3513441150Moisture and gases seperating(low condensation on glass)offMoisture and gases seperating(low condensation on glass)272.5
10:4113232056low gases and vapor condensation observedofflow gases and vapor condensation observed226
10:5013645665more gases startedonmore gases started10:50 – 10:4505 min.296
10:5816051073Chimney tip changedoffChimney tip changed335
11:0515736980no gas, no vaporsoffno gas, no vapors263
11:1216250287condensed drops coming no gasoncondensed drops coming no gas11:12 – 11:0606 min.332
11:1417551089gas without moistureoffgas without moisture342.5
11:25:35192534100.5on11:25:35 – 11:2104 min. 35 sec.363
11:30215550105no gas, no vaporsoffno gas, no vapors382.5
11:41258722116gases startedongases started490
11:43269745118gas flow increasedongas flow increased507
11:45286769120flame starting, condensation happens and drops at 1st hole observedonflame starting, condensation happens and drops at 1st hole observed527.5
11:52:30348837127.5Flame short breakingonFlame short breaking592.5
12:02:30405911137.5flame sustaining very long but gases breakingonflame sustaining very long but gases breaking658
12:33499995168flame breakingonflame breaking12:33 – 11:3102 min.747
12:40501973175no condensation550onno condensation737
12:595371023194on12:59 – 12:4019 min.780
13:175561023212trial end500ontrial end13:17 – 13:0710 min.789.5
Trial 6
Image: Time Vs. Temperature curves on Inside chamber (Pyrolysis Chamber) and outside chamber

Trial Outcomes –

  1. Trial on 7 wet or soiled pads using water performed.
  2. Trial completed in 3 hour 32 minutes.
  3. Heaters running time is 63 minutes which consumed 4 kw. electricity.
  4. With loading 7 wet pads energy cost per pad was INR 5.5.
  5. This trial is an optimization as compared with previous trial.
  6. During the trial condensed grease like liquid noticed at the tail of chimney.
  7. T joint was placed at the end of chimney with cotton on bottom side for absorbing condensate while other side of the T-joint was exit of gas and starting of flame.
  8. The drying time was around 155 minutes out of 312 minutes during trial.
Image: Chimney with T joint and cotton for condensate absorption
Image: Ash remained after trial

Brainstorming and analysis of trials data done with Dr. Arun Dixit, Mr. Ameya Kulkarni and team.

Suggestions and modifications received during discussion –

  • To make hollow space at the center of inside pyrolysis chamber to reduce drying time by shortening the heat transfer length.
  • To limit or specify the capacity of the current prototype to 7 pads disposal at maximum per batch.
  • To work on reducing energy consumption per pad for disposal.

Trial 7 – Trial on 7 wet pads

Trial 7         Wet Pads                                                               Date – 19/01/2019                                             Wet Pads                                                               No. of Pads- 07                                                      Weight of Pads                                   ( Before Incineration)                              1. Sample S1 – 6.84 gms                 2. Sample S2 – 7.00 gms                 3. Sample S3 – 6.87 gms                 4. Sample S4 – 6.76 gms                 5. Sample S5 – 6.77 gms                 6. Sample S6 – 6.84 gms                 7. Sample S7 – 6.66 gms           Total Weight of Pads – 47.74 gms                                                                    Weight of Water Added                                              (approx. 50 % by weight)                                                                                        1. In S1 – 6.78 gms                                     2. In S2 – 7.38 gms                                     3. In S3 – 7.16 gms                                     4. In S4 – 6.76 gms                                     5. In S5 – 6.80 gms                                     6. In S6 – 6.76 gms                                     7. In S7 – 6.89 gms                               Total Weight Of Water added – 48.53 gms
Time Inside Chamber TemperatureSurface Temperature Heaters Run timeSet TemperaturesHeaters StatusComments
15:18544538 min
15:2178496very few gases andvapors
16:0015862028 minoffgases with moisture
16:20165329gases and vapors stopped
16:35163424very low gases coming
16:3716757413 minoff
16:56260766gases increased
17:00300836flame starting
17:44455998flame breaking
17:5041376463 minheaters fusedGases stopped completely
Image: Time Vs. Temperature curves on Inside chamber (Pyrolysis Chamber) and outside chamber
  • As per discussion wet pads loading cage is modified by placing hollow cylinder at the center made up of wire mesh.
  • Trial started on 7 wet pads.
  • During trial drying observed for around 80 minutes and gases started coming out without moisture.
  • Moisture in gases checked by placing transparent glass in gas flow.
Image: Modified loading cage
Image: Moisture condensed from gas

During this trial the IR ceramic heaters run at above maximum permissible temperatures due to which all 8 heaters fused. It was required to run the heaters at higher temperatures since, the temperature difference was 350° C during the 7 pads trial and pyrolysis temperature range achieved from was in between 450° C to 600° C.

Image: Fused IR ceramic heater
  • The diagnosis of heaters fusing highlights following reasons
  1. Running the heaters at above maximum permissible temperature range.
  2. The gap between heater surface and pyrolysis chamber surface.
  3. Front facing arrangement of heaters with very low distance in small vicinity.
  4. The heaters procurement without datasheet or operating manual, etc.

Please click here to understand the operation of current prototype:

Bill of Material –

Sr. No.DescriptionMaterial/DetailsNo. of UnitsMaterial QuantityVendor
1Pyrolysis chamberMS CRCA sheet 2.5 mm thickness 14 sq. feetLocal steel trader
2Pyro. chamber flange MS CRCA sheet 2.5 mm thickness 14 sq. feetLocal steel trader
3Pyro. chamber bottomMS CRCA sheet 2.5 mm thickness 12 sq. feetLocal steel trader
4Outer shellMS CRCA sheet 2.5 mm thickness 15 sq. feetLocal steel trader
5Outer shell bottomMS CRCA sheet 2.5 mm thickness 12 sq. feetLocal steel trader
6LidMS CRCA sheet 2.5 mm thickness 15 sq. feetLocal steel trader
7GasketCompressed Asbestos jointing sheet 3 mm thick13 sq. feetMfg. by – Samsonite,Shah Rubber products Bhosari
8Wing nut and boltsM6* 4 inch44
9IR Ceramic heatersCeramic IR curved type 122mm*60mm*500watt* 240 V AC88BK Electricals Vashi, Navi Mumbai
10J type industrial thermometersJ type 100 mm probe 1160 degree Celsius with module22Bombay Electricals and Engineers Pune
11Temperature controllerSelec TC51311Bombay Electricals and Engineers Pune
12Solid state relaySSR11Bombay Electricals and Engineers Pune
13MCB2 pole 32A11Bombay Electricals and Engineers Pune
14ChimneyMS Pipe – 2 inch dia. * 2 mm thick11 feetLocal steel trader

Pyrolysis based sanitary napkins incinerator Version 3.2

Background –

After performing the trials and heaters burnout or fusing in V3.1, it is decided to design a new prototype considering the results of previous experiments data and understandings.

Key learning from experiments with previous prototype (v3.1)

  • With available ceramic IR heaters and design it is difficult to achieve and maintain pyrolysis temperature range of above 450 degree Celsius inside the pyrolysis chamber.
  • To maintain 450 degree Celsius inside the pyrolysis chamber heaters required to run by adding 250 degree Celsius temperature difference at chamber outer surface and center.
  • In previous prototype (V3.1) indirect heating is used. Heat loss occurs in heating and cooling of pyrolysis chamber material.
  • Due to indirect heat transfer cycle time for disposal of soiled pads increases which leads to high energy consumption.

Objectives with current prototype v3.2

  • To reduce cycle time required for complete disposal of soiled pads using pyrolysis principle.
  • To reduce energy consumption for given batch.

By considering above objectives for designing and developing the prototype the cost requirement of disposal per pad will also reduce.

Concept and Assumptions

  • The heat required for heating of pyrolysis chamber with indirect heat transfer to soiled pads will be reduce by placing Ceramic IR heaters inside the pyrolysis chamber.
  • Direct heating will reduce the heat loss and cycle time of a batch.
  • The operating temperature of heaters will not exceed its maximum permissible temperature range.

Following is the concept sketch with modifications including

  • Ceramic IR heaters inside the pyrolysis chamber
  • Soiled pads inlet arrangement
  • Central exhaust/chimney at the top of incinerator
  • Ash removal arrangement with independent bottom platform
Image: Pyrolysis based sanitary napkin incinerator v3.2 (Concept sketch)
Image: Cross section view of concept
Image: Details of conceptual model cross section
Image: Concept picture

Detailed Design

Design Considearations

  • Capacity of pyrolysis chamber – 5 soiled pads when bundled
  • Material – MS CRCA sheet 2.5 mm thickness
  • Split design with 3 assemblies
    • Base assembly – Consist of cage and bottom lid as base which is removable for ash removal.
    • Main chamber assembly – Consist of pyrolysis chamber with internally mounted ceramic IR heaters. Removable outer cover with glass fibre insulation and heater mounting arrangements.
    • Chimney – Consist of pyrolysis gases exaust and flame arrangement. Also having pad loading door. Chimney is also removable and a independent assembly.
  • Loading cage volume – 1.871 liters

CAD and detailed drawings

  • Base Assembly
Image: Base assembly

Base assembly includes-

  1. Base plate

Two base plates are required to make complete base.

Image: Base CAD
Image: Base detailed drawing

2. Base Flange

Image: Base flange CAD
Image: Base flange detailed drawing

3. Cage

Cage is based on upper base plate for the purpose of loading pads.

Image: Cage CAD
Image: Cage detailed drawing
  • Main Chamber Assembly
Image: Main chamber complete assembly CAD

Main chamber assembly is the core of complete incinerator model which includes;

  1. Pyrolysis chamber
Image: Pyrolysis chamber cAD
Image: Pyrolysis chamber detailed drawing

2. Outer chamber

Image: Outer chamber CAD
Image: Outer chamber detailed drawing

3. Chamber Flange

Image: Chamber flange CAD
Image: Chamber flange detailed drawing

4. Main chamber top flange

Image: Main chamber top flange CAD
Image: Main chamber top flange detailed drawing

5. Outer chamber support

Image: Outer chamber support CAD
Image: Outer chamber support detailed drawing
  • Chimney

Chimney assembly consists of loading door, chimney outlet for pyrolysis gas escape and flame purpose. This assembly is independent which is removable and joint is sealed using gasket.

Image: Complete chimney assembly CAD

This includes;

  1. Chimney bottom flange
Image: Chimney bottom flange CAD
Image: Chimney bottom flange detailed drawing

2. Chimney middle flange

Image: Chimney middle flange CAD
Image: Chimney middle flange detailed drawing

3. Chimney top flange

Image: Chimney top flange CAD
Image: Chimney top flange detailed drawing

4. Chimney outer support

Image: Chimney outer support CAD
Image: Chimney outer support detailed drawing

5. Chimney outer chamber

Image: Chimney outer CAD
Image: Chimney outer detailed drawing

6. Chimney top

Image: Chimney top CAD
Image: Chimney top detailed drawing

7. Loading point

Image: Loading point CAD
Image: Loading point detailed drawing


  • Sheet cutting and cylindrical chambers

Using above design details and CAD models manufacturing of the prototype started. CNC plasma cutting machine and sheet metal rolling used mostly for manufacturing. Arc welding used for joining operations.

2 mm thickness MS CRCA sheet is used.

Image: Sheet cutting by CNC plasma cutting machine
Image: During sheet cutting

After cutting rolling operation done for making cylindrical parts like outer chamber, pyrolysis chamber, chimney outer chamber.

By using arc welding joining operations done as per CAD drawings.

  • Heater mounting and main chamber assembly

Ceramic IR heaters 2 nos. mounted inside the pyrolysis chamber and the mounting surface is made leak proof using thermal sealant.

The heaters are of 500 watt each. Gap between pyrolysis chamber surface and outer chamber is filled by glass wool as an thermal insulation to avoid heat loss. Outer chamber is removable with purpose of heaters handling and maintenance.

Image: Heater mounting in pyrolysis chamber
Image: Main chamber with heater mounted

Compressed asbestos jointing sheet gasket is used between two joining surfaces for leak proof joint.

  • Chimney assembly with inlet door, chimney and loading cage

This assembly includes inlet door with wing nuts for loading of soiled sanitary pads. Central gas exhaust arrangement in top flange given as chimney where flame can be made for disposing the gases from pyrolysis.

The cage is provided with perforation and open at bottom. Following image shows complete chimney assembly.

Image: Chimney with loading inlet, gas exhaust and loading cage
  • Sanitary napkin incinerator prototype v3.2 complete assembly
Image: Complete incinerator (v3.2) assembly

Testing and Trials

  • Trial 1

Trial 1st is performed as a test run without any pads or materials to check functionality of the prototype.

During this trial maximum temperature of 540 degree Celsius achieved inside the pyrolysis chamber in 35 minutes using two heaters 500 watt each.

With the result of temperature range achieved in test trial next trial on two soiled pads using water scheduled and performed.

Image: During test trial
  • Trial 2

This trial is performed for two sanitary napkins soiled in water with same quantity by weight.

Initially drying of pads started and continued for 35 minutes in the temperature range of 100 degree Celsius to 160 degree Celsius. Temperatures set at 500 degree Celsius when dry gases started coming out of the chimney.

Maximum temperatures achieved of 385 degree Celsius after which temperature range started falling down. Temperatures doesn’t increased for next one hour and trial has stopped.

Image: Trial 1 on two wet sanitary napkins

Diagnosis done for not raising temperature during the trial inside the pyrolysis chamber. Heaters found fused in the chamber.

Image: Heaters and pyrolysis chamber after trial
Image: Heater fused

After this trial it is decided to not use electrical heaters directly inside the pyrolysis chamber.


After performing trials on two versions it is understood that electrical heating for pyrolysis based incineration is costly and not reliable with available heaters for the v3.1 prototype design and v3.2 also.

Material of construction study is required considering optimum heat transfer for pyrolysis.

It is also decided to work on design of a prototype of gas based heating system for incinerator and recirculation of gases from pyrolysis of soiled pads.

The gas fired pyrolysis based sanitary pad incinerator concept sketch is given below.

Image: Concpt sketch of gas fired pyrolysis based sanitary napkin incinerator

Following is the link for downloading all DXF files for manufacturing –