Biodiesel Properties of Concern

C.R. Krishna, Brookhaven National Lab

John Batey, Energy Research Center Inc

BIODIESEL WORKSHOP 2008

May 2, 2008

Biodiesel properties of Concern

Currently there is a fuel standard for biodiesel• ASTM D 6751 which is undergoing some changes• The standard applies irrespective of the source material, that

is the starting oil or fat- At present, most biodiesel in the U S is made from soy oil

We have found that there are differences in two properties between biodiesels made from different source materials• These properties are not presently specified in the standard• They are important to the use of biodiesel in heating• The two relate to cold flow and flame Sensing in Boilers

Biodiesel properties of Concern-Cold Flow

Cold Flow Properties• Usually defined by cloud point or pour point

- Temperature at which some of the components in the fuel start to freeze or when it cannot be poured

- Typical cloud point temperature for heating oil is well below 00 C or 320 F

- The cloud point temperature for biodiesel made to ASTM 6751 depends on the source material and can be well above 320 F

Biodiesel properties of Concern

Cloud Point Temperatures of Neat Biodiesel

-4

-2

0

2

4

6

8

10

12

14

16

Soy Tallow Yellow Grease Canola

Fuel Types

Temperature C

Biodiesel properties of Concern

Cloud Points of soy and yellow grease biodiesel blends

0

2

4

6

8

10

12

100% Yellow Grease 80% Yellow Grease 50% Yellow Grease 20% Yellow Grease 100% Soy

Blend Ratio between Soy and Yellow Grease

Clo

ud

Po

int

Te

mp

era

ture

C

20% Soy 50% Soy 80% Soy

Biodiesel properties of Concern

No. 2 oil blends vs. Cloud Point Temperature

-25

-20

-15

-10

-5

0

5

10

15

20

0 0.2 0.4 0.6 0.8 1

Fraction Biodiesel

C

lou

d P

oin

t, D

eg C

Soy

Yellow Grease

Tallow

Biodiesel properties of Concern-Cold Flow

Conclusions from Cold Flow Properties of different biodiesels• The source material affects strongly the cloud points• Even small amounts in blends can affect transport, storage and

use in boilers• Hence, it may not be enough to specify just ASTM 6751 for

buying biodiesel blends

We acknowledge the help of summer students, Christopher Brown and Kaitlin Thomassen in making measurements• See Publication in Ind. Eng. Chem. Res. 2007, 46, 8846-8851 for

details

Biodiesel properties of Concern - Flame Sensing

Project to evaluate how different biodiesels and their blends with heating oil impact the cad cell system operation• The cad cell senses the presence or absence of flame

- Based on this, the control system keeps the burner on or turns it off

• It had been observed that oil burners firing biodiesel may shut off even when the flame was stable and this was traced to the cad cell control system

• Phase I tests found high cad cell resistance for higher percentages of Biodiesel in #2 oil and for higher excess burner air settings.

• Phase II test found cad cell resistance varies with burner manufacturer

• Project was funded by the National Biodiesel Board

Biodiesel properties of Concern – Cad cells

Biodiesel properties of Concern – Cad cells

Key Points:

• The cad cell resistance at high burner excess air varies with the type of biofuel used.

• Conventional oil burner cad cells that sense the presence of a flame cannot be used for high blends ratios of many biofuels.

• Soy biofuels produce the highest resistances, followed by Canola Oil, Tallow3 and Soy/ Tallow blends, and Yellow Grease.

• These finding are also important because they can be used as a new test method for identifying the type of biofuel being used.

Biodiesel properties of Concern

Biodiesels made to ASTM 6751 from different sources were tested

• Two different burners in two residential boilers were tested • The resistance of the cad cell is used by the control

• Resistance higher than set value triggers burner shut down

• Cad Cell resistances while the flame is present of 1500 to 1600 Ohms is usually desired

• So, cad cell resistance was measured during burner operation on different blends and varying burner excess air settings

Cad Cell Resistance VS. Excess Air(SoyPower Diesel)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 50 100 150 200 250 300 350 400

Time from Burner Readjustment (Sec)

KO

hn

Re

sis

tan

ce

- C

ad

Ce

ll

10.6% O210.1% O28.9% O27.2% O26.2%O25.4% O24.4% O23.4% O2

Changes in Cad Cell Resistance with Burner Excess Air

Biodiesel properties of Concern

Conclusions - Flame Sensing and Control

• A new field test can be developed using cad cell output to determine the type of biofuel in a sample

• The Cad Cell resistance varies with the type of biofuel used, its blend ratio in heating oil, and the excess air setting of the burner

• Soy-based biodiesel percentages may be limited to low blend ratios and low excess air settings, or alternate flame sensing devices may be needed

• Burner design has an important impact on cad cell resistances and compatibility of conventional cad cell flame sensors with biodiesel blends

• More research is needed to fully develop these relationships and determine solutions for the use biofuel blends.